Fiona · Engineering experiments, shipped with care

01 · Projects

Projects

Eleven recent projects from my GitHub, by topic. Each one runs, is open source and documented: open the details for more screenshots, how it is built, and links to its docs, releases and packages.

Games

Puzzles and a 3D game, all made for the browser.

Gadget No. 01 since Nov 2026

Wormhole Surfing Link to Wormhole Surfing

A 3D browser game: surf a wormhole on a cute spaceship and warp into strange worlds full of treasure.

Why: How far does code alone go? Not a single image, model or sound file: the ship, the chibi pilot, eight worlds, the music and every sound are generated in code, and the whole game still has to hold its frame rate on a phone.
What: Steer through a swirling tunnel, collect orbs for speed, dodge sparks and pick a warp hole before one picks you. Behind it, the pilot explores a world on foot and opens the treasure waiting there; rarer holes and longer rides bring rarer finds for the collection.

Runs on

Browser
Offline & installable
Android

Open it Android app (APK) Source

More screenshots

The ride: light-years flown, speed, orbs, sparks and warp holes
Arrived in the Lagoon, with the compass pointing to the treasure
The star capsule opens in the light of the treasure’s rarity
What it held, how rare it is and whether it is new

What it does

Eight worlds, from the Lagoon to the Aurora Void, each with its own sky, terrain, water, plants and music.
Forty treasures in five rarities, shiny variants, and a collection that can be shared as a picture.
Plays with keyboard, mouse, game controller, touch sticks or by tilting the phone.
A cockpit HUD with a speed gauge and seven-segment displays drawn in SVG.
Installs as an app and plays offline; the Android app updates itself from GitHub releases.

Under the hood

Game rules as pure, deterministic TypeScript at 120 steps a second, kept apart from three.js and the interface.
A render pipeline with bloom, guards against broken HDR pixels and adaptive resolution; worlds are built in steps during the warp and their shaders compiled ahead, so arriving never stalls.
Music generated bar by bar from a mood, every effect synthesized with Web Audio.
Playwright tests play whole rides with WebGL in software, a weekly soak test hunts memory and GPU leaks, and unit and browser coverage go to Codecov.

Links

Gadget No. 02 since Oct 2026

Vibe Puzzles Link to Vibe Puzzles

Six logic puzzles with unique solutions, generated on the device, with hints that explain the next step.

Why: Puzzle apps like to hide their best puzzles behind ads and subscriptions. Here, deterministic algorithms make every puzzle with a guaranteed unique solution, and when you are stuck, a hint shows not just what to do next but why.
What: Tetroid, Pinwheel, Sudoku, Calcudoku, Loop and Pipes in several sizes and levels, plus daily, weekly and monthly specials. A puzzle ID gives the same puzzle on every device, and an optional server syncs progress and ranks solves.

Runs on

Browser
Offline & installable

Open it Source

More screenshots

Tetroid, half solved
Pinwheel: regions symmetric around their circle
Loop, with crosses around the zeros
Pipes: water fills every joined pipe
A 7×7 Calcudoku
A hint: where to look, the step, and why
A trial in teal, with Keep and Discard
The Halloween look by night
Widescreen on a tablet in landscape
On a phone, in German, by night

What it does

Hints in two stages: first where to look and which rule applies, then the step that follows from your own marks.
Trials: try an idea in teal, then keep or discard it as a whole.
Undo, checkpoints, notes, error highlighting, timers, zoom, keyboard and touch controls.
A guided tutorial for every game, and an Inside page that shows as a film how a puzzle is made.
Seasonal looks for Halloween, winter and Christmas, each by day and by night.

Under the hood

Deterministic generators and solvers that prove every puzzle has exactly one solution, plus a pre-generated puzzle bank.
SvelteKit as a static PWA on GitHub Pages, or with an optional server on Cloudflare Workers and D1 for sync and scores.
Nothing deploys before lint, type checks, unit, browser and server tests pass; accessibility is checked with axe, and load and soak tests run on a schedule.

Links

Gadget No. 03 since Oct 2026

Vibe Laser Link to Vibe Laser

A laser logic puzzle: place mirrors, prisms and filters until every coin is lit in exactly its color.

Why: A love letter to the puzzle classic Aargon Deluxe (2001): its rules rebuilt from a written specification, with an original name, art and levels, so that it plays like the original without copying it.
What: Nineteen optical parts, from mirrors and prisms to color converters and polarizers, and six hazards and actors: explosives, fuel cells, black holes, slimes, robot mines and spaceships. Seven level packs, a level editor, and levels that travel as links.

Runs on

Browser
Offline & installable

Open it Source

More screenshots

Seven level packs, from the Tutorial to Powder Keg
Each pack chooses its skill on a screen of its own
While a piece is carried, faint beams show where its light would go
Explosives, fuel cells and black holes in the Neon look
A hint outlines where the next piece goes
Color-blind mode: colors as letters, each color its own line
The level editor
On a phone held sideways, the buttons sit beside the board

What it does

A live preview: while a piece is carried, faint beams show where its light would go.
Hints & Solutions shows where the next piece goes, or plays the whole solution.
A color-blind mode that writes colors as letters and draws each color in a beam as its own line.
Mouse, touch with pinch zoom, keyboard and game controller, with every binding changeable.
Profiles with their own progress and settings, moves and par per level, export and import.

Under the hood

The beam model as pure TypeScript with property-based tests (fast-check); PixiJS 8 only draws it.
Level packs checked by Zod schemas, with JSON Schemas generated from them for editors.
Offline through a service worker plugin of its own for Vite; the README screenshots are taken by Playwright in CI.

Links

Networking & peer to peer

Devices that talk to each other directly, and a tunnel for servers behind a router.

Gadget No. 04 since Nov 2026

Spielekiste Link to Spielekiste

Board, card, dice and party games for phones side by side, connected directly by QR code, without internet or a server.

Why: A game night shouldn’t need accounts, ads or the Wi-Fi password. A box of classics where the phones on the table talk directly to each other, over a hotspot or by Bluetooth, and nothing leaves the table.
What: Twenty-two games of four kinds: tactics such as Nine Men’s Morris, Draughts and Chinese Checkers; luck and bluff such as Ludo, Mäxchen and Werewolf; party games such as City, Country, River; and real-time games such as Light Racers and an air hockey rink that runs across two phones. Up to eight phones sit at a table, or two to six players share one laptop.

Runs on

Browser
Offline & installable
Android

Open it Android app (APK) Source

More screenshots

The game chooser on a laptop
Ludo for up to four
Mäxchen: only the roller sees the dice
City, Country, River: checking the answers
Light Racers: each phone steers its own rider
Air hockey
Miau-Miau for four on a split screen
Pairing by QR code
Themes, here with the seasons: Halloween

What it does

Pairing by QR code over any Wi-Fi or a phone’s hotspot, or by Bluetooth in the Android app.
Hidden cards stay hidden: the host decides everything and sends each phone only what it may see.
The rules of every game step by step with drawings, in English and German.
Themes from wood and green felt to neon that follow the seasons, and stickers on queer and trans days of visibility.
No accounts, no tracking, no ads; installable and playable offline.

Under the hood

Built on @fionapreroll/p2p and @fionapreroll/p2p-nearby, the networking libraries that grew out of Spark Hunt.
Real-time games over the same peer-to-peer connection; the air hockey puck is smoothed with a Kalman filter.
Browser tests in Chromium over real WebRTC connections, unit and browser coverage on Codecov, and an Android APK built by CI on every push.

Links

Gadget No. 05 since Oct 2026

PortRedirect Link to PortRedirect

Glue your frontend to the backend: a lightweight TCP forwarder that tunnels connections over QUIC.

Why: A home server behind a router can’t be reached from outside. PortRedirect lets a small, cheap public server take the connections and pass them through an encrypted tunnel that the home server opens itself: no port forwarding, and almost as if the big machine were on the internet.
What: The server listens for TCP connections, on port 443 for example, and tunnels each one as a stream over a persistent QUIC connection; the client hands it to the target service, such as localhost:8443. Both sides authenticate with a pre-shared key, and the client pins the server’s certificate.

Runs on

Linux
Docker

Releases Source

More screenshots

A browser reaches a home server through the QUIC tunnel
For comparison: a direct TCP connection
The crate’s modules and how they depend on each other

What it does

Several clients with standby, reconnects, graceful shutdown, and reloading the configuration on SIGHUP.
Limits per client address, and Prometheus metrics.
Configured by a TOML file or environment variables.
Prebuilt binaries for Linux on amd64, arm64 and armv7, with glibc or static with musl, and Docker images for all three.

Under the hood

Rust with Tokio, quinn for QUIC and rustls; a documented wire protocol and a written security review.
Fuzzing, cargo-deny, CodeQL and dependency audits in CI, with coverage from cargo-llvm-cov.
End-to-end tests and benchmarks with iperf3 and netcat, BATS tests, and builds tested on each architecture before every snapshot release.
Release binaries with SHA256 sums and attestations of where they were built.

Links

Gadget No. 06 since Oct 2026

Spark Hunt Link to Spark Hunt

A real-time game for phones lying side by side, with no internet and no server, not even to connect.

Why: The project is about the connection: can phones play together in real time with no server at all, not even for signalling? The game is small on purpose, and the networking grew into three libraries that other apps use now.
What: Every player steers a glowing dot, and whoever reaches a spark first scores, while mines cost points. The phones swap their WebRTC offers by scanning each other’s QR codes over a shared Wi-Fi or hotspot, or connect by Bluetooth in the Android app; up to eight play together.

Runs on

Browser
Offline & installable
Android

Open it Android app (APK) Source

More screenshots

Adding a player by QR code
After a round: who caught what
The connection details, after a connection test
Keys and controller buttons, changeable
In German

What it does

A live connection graph with ping, a connection test under load, and a debug report without names or addresses.
Players who drop out, even the host, rejoin and get their place and score back.
QR scanning made for screens: tap to focus, zoom, brightness, switching cameras, or text codes without a camera.
A color and a shape for every player, so the dots stay apart for color-blind players too.

Under the hood

@fionapreroll/p2p: codes, WebRTC, connections over any transport, rooms and QR codes.
@fionapreroll/p2p-nearby: Bluetooth for Capacitor apps through Google’s Nearby Connections, written in Java.
@fionapreroll/app-updates: updates of Android apps from their own GitHub release, with pause and resume.
All three published on GitHub Packages; Playwright tests over real WebRTC, and property-based tests with fast-check.

Links

Music & audio

Making, playing, hearing, showing and remembering music.

Gadget No. 07 since Nov 2026

AudioRef Link to AudioRef

A VST3 and CLAP plugin that evens out your headphones, so that budget and consumer models sound closer to neutral studio monitoring.

Why: Mixing on a Bose QC25 or a Sony WH-1000XM4 means mixing against their bass and treble. Measurements and correction curves for them exist; AudioRef puts them where the mix happens, as the last plugin on the master, with no latency, no clipping and no way for the correction to slip into an export.
What: Pick your headphones and an EQ preset from OPRA, built in for the Bose QC25, the Sony WH-1000XM4 and the AKG K240 Studio, or loaded from OPRA’s database for thousands of others. Or load a measurement and a target curve in AutoEQ’s format, and AudioRef designs the correction itself, to be adjusted with tilt, bass and a limit for boosts.

Runs on

Windows
macOS
Linux

Releases Source

More screenshots

A correction designed from a measurement and a target, with tilt, bass and the limit for boosts, in linear phase with 43 ms of latency
A preset from OPRA’s database, loaded from a file
The hint of the crossfeed, with the pointer resting on it
Opened for the first time: the headphones with built-in presets, and what to do next

What it does

Automatic headroom: when a correction boosts some frequencies, AudioRef lowers its level by as much, so nothing gets louder, and a limiter without latency keeps the output below −0.3 dBFS.
Bypasses itself when the DAW exports offline, so the correction stays in the monitoring path.
Linear phase on request: the correction keeps transients in shape, and AudioRef tells the DAW its 43 to 46 ms of latency, so the tracks stay in time.
Crossfeed in three strengths, mono and swapped channels, to hear a mix a little more as from speakers and to check it in mono.
The project saves the correction, so it opens the same on a computer without the files; every change fades over 20 ms, so nothing clicks.
A window with the frequency response of the correction, a level meter, hints on every control, and the author of each preset, in English and German.

Under the hood

Rust with nih-plug and egui; the signal processing is a crate of its own without plugin APIs, tested to 100 % of its lines and functions.
The audio thread never allocates, locks or reads files: filters are designed in the background and handed over through lock-free queues, and the old ones go back to be freed.
Matched biquads that hold up to the highest frequencies at every sample rate, minimum-phase FIR filters from the real cepstrum, convolved in partitions without latency, and linear-phase ones whose latency the DAW makes up for.
Bundles for Windows, macOS and Linux, checked with clap-validator and pluginval at strictness 10; weekly fuzzing of every file it reads, cargo-deny, CodeQL and zizmor in CI, and screenshots of the window taken on a virtual display.

Links

Gadget No. 08 since Oct 2026

Vibe Soundlab Link to Vibe Soundlab

Drum & bass and chiptunes written as code in Strudel, and a browser player with a mixer, live chords and visuals.

Why: Music as code: writing tracks in Strudel, then building the player I wanted for them, with a real mixer, the chords to play along on guitar, and visuals that follow each track’s arrangement.
What: Thirteen tracks, from atmospheric rollers and bangers to keygen, C64 and Amiga-style chiptunes, each a plain Strudel file that runs on strudel.cc too. The player shows the parts of every track, outlines the notes that sound in the code, and lets you change the code while it plays.

Runs on

Browser

Open it Source

More screenshots

The progress bar with the parts of the track
The mixer, with the EQ curve over the bass’s spectrum
The code, with the notes that sound right now outlined
A mistake typed while it plays: the line is marked, the music goes on
The guitar chords, now and next, with their fingerings
Visuals of Polarlicht
Visuals of Kernschmelze
Visuals of Nachtschicht
Songs other people share on GitHub

What it does

A mixer with a channel per orbit, mute, solo, live spectra and an 8-band EQ.
Guitar chords worked out live from the playing pattern, with a fingering for every chord.
Live editing as on strudel.cc: Ctrl+Enter swaps in the new code without restarting the track.
Hydra visuals for every track, driven by its energy and beat.
Your own Strudel files, and songs other people share on GitHub, play next to them.

Under the hood

A guard keeps mistakes from taking the page down: syntax checks before code runs, loop guards, and limits for runaway patterns.
Every orbit gets its own output channels, split back up in a Web Audio graph of its own.
No build step: plain JavaScript modules, tested on Node’s test runner with coverage limits, including every track’s header, arrangement and chord shapes.

Links

Gadget No. 09 since Oct 2026

musicbanana Link to musicbanana

A free, self-hosted home for your listening history: scrobbling, charts, reviews and statistics.

Why: A project that has been running in one form or another since 2007. A listening history is personal and worth keeping, so musicbanana keeps it on your own server: rebuilt from the 2016 PHP version as a small Rust server with a Svelte interface, and the old database comes along.
What: It takes the plays of every player that speaks the ListenBrainz API, such as Navidrome, and of Spotify through YourSpotify, and turns them into profile pages, charts for any period with their movement, a year in review, a listening clock and comparisons of two profiles.

Runs on

Self-hosted
Docker
Browser

Docker image Source

More screenshots

Charts for any period, with their movement
A year in review
Comparing two profiles
A page for every album
The listening clock: plays by weekday and hour
Lost & found: heard a lot, but not for a year
Top artists over the years
The dark theme
On a phone
Suggestions for merging two spellings

What it does

Charts for any period with arrows for their movement, Lost & found, and top artists over the years.
Several accounts and profiles, each public, for followers or private, with follows and a trash for wrong listens.
A tidy catalog: suggestions for merging spellings of the same artist, album or track, with undo.
Album covers from the Cover Art Archive, English and German, light and dark.
A download of all your data, and an importer for the 2016 PHP database with its accounts.

Under the hood

Rust with axum, sqlx and PostgreSQL, with SQL queries checked at compile time.
A SvelteKit interface with Tailwind CSS, built statically and served by the Rust server.
Integration tests on fresh databases, property tests with proptest, and component tests with Testing Library; coverage on Codecov.
A Docker image on GitHub’s container registry, and a Compose setup to run next to Navidrome.

Links

Gadget No. 10 since Sep 2026

FibeStation Link to FibeStation

An audio-reactive music visualizer that renders HD videos for YouTube and TikTok, right in the browser.

Why: Music deserves pictures, but video editors are heavy and online tools want your files. FibeStation makes both live visuals and finished videos on your own machine: no server, no uploads, rendered frame by frame and smooth on any computer.
What: Two looks follow the beat: a logo in a glowing spectrum ring, and kaleidoscopic feedback tunnels with neon tubes, each with presets that switch with the music. Around them sits a player made for DJs, with a gapless queue, waveforms, hot cues, a beat grid, tempo with key lock and effects.

Runs on

Browser

Open it Source

More screenshots

The Kaleidoscope’s Vortex scene
Neon Ribbons: tubes of light, rings and soft lights
Rain instead of stars, in a wind
9:16 for TikTok, with its safe areas
The analysis: what the visuals react to
Tempo, filter, delay, reverb and Slowed + Reverb
The queue as one video, with chapters
A DJ controller, connected
The mini player, on top of other windows

What it does

MP4 exports in 1080p60, 4K30 or 1080×1920 of a track, a clip or a whole queue with YouTube chapters, resumable after a crash.
Live input from a DJ mixer, an audio interface, another app or a browser tab.
DJ controllers over Web MIDI, with their lights, and MIDI learn for other controllers.
A mini player that stays on top of other windows, and a second screen for a projector.
Visuals in the colors of the cover art, and a backup file for settings, presets, cues and images.

Under the hood

An audio engine on AudioWorklet with SharedArrayBuffer ring buffers, and time stretching by Signalsmith Stretch in WebAssembly.
WebGL2 rendering in a worker, hardware video encoding with WebCodecs, and beat tracking evaluated on real recordings.
End-to-end tests in Chromium and Firefox in eight parallel jobs, plus soak and performance tests with traces.
A DJ controller library of its own, and the licences of every bundled package collected by the build.

Links

Everyday

Small tools that simply work.

Gadget No. 11 since Sep 2026

Vibe-Stundenplan Link to Vibe-Stundenplan

A weekly timetable in the browser: no account, no backend, no build step.

Why: A timetable for a university week that simply works: open it, fill it in, done. Everything stays in the browser, and the code stays small enough to read in an afternoon.
What: A weekly grid with days to rename, add and remove, time grids from presets such as TU Dresden and RWTH Aachen or fully custom, entries by click or by dragging across slots, and several schedules side by side, exported as readable JSON.

Runs on

Browser

Open it Source

More screenshots

Dark mode, with editing locked
Adding an entry
Setting the time grid

What it does

The current time slot and weekday light up as the day goes by.
Entries with their own start and end times, independent of the grid.
Fully usable by keyboard; light, dark and system theme; a one-tap lock for a clean read-only view.
German and English, chosen from the browser’s language.

Under the hood

Plain JavaScript modules without dependencies, tested with Node’s built-in test runner; CI fails below 95 % coverage and reports it to Codecov.
A small Playwright suite guards the layout, and CI takes the screenshots again on every push.
Requirements, the export format and design decisions written down in the repository.

Links

02 · How I build

How I build

The same habits run through all of these projects. Each tile names where they show best.

Typed end to end

TypeScript in strict mode, Rust where it counts, and schemas at every border where data comes in: saves, level packs, imports and the network.

Seen in Vibe Laser Wormhole Surfing PortRedirect FibeStation
Tested in real browsers

Unit tests with Vitest, Playwright tests that play the actual app, property-based tests, soak tests that hunt memory leaks, and accessibility checks with axe.

Seen in Wormhole Surfing Vibe Puzzles FibeStation Spielekiste
CI on every push

GitHub Actions run type checks, lint, tests and coverage on every push. Deploys wait until everything is green, and CI builds the screenshots, Android apps and release binaries.

Seen in Vibe Puzzles PortRedirect Spark Hunt Vibe Laser
Offline, private, installable

Web apps that keep working without a connection, install like apps and keep data on the device. Capacitor turns them into Android apps that update from their own GitHub releases.

Seen in Spielekiste Spark Hunt Wormhole Surfing FibeStation
In two languages

Every text in English and German, with typed catalogs, so that a missing translation fails the type check instead of showing up on screen.

Seen in Wormhole Surfing Vibe Laser Vibe Puzzles musicbanana
Written down

READMEs that explain how things work and why, architecture and protocol documents, decision records, and changelogs in the Keep a Changelog format.

Seen in PortRedirect Spielekiste FibeStation Vibe-Stundenplan

03 · Tech

Technologies

Everything these projects are built with, by how many of them use it. Pick one to see its projects.

04 · Contact

Get in touch

A role, a project, or a question about one of these: I’m happy to hear from you.

Engineering experiments, shipped with care.

Games

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What it does

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Networking & peer to peer

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Music & audio

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Everyday

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Under the hood

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Typed end to end

Tested in real browsers

CI on every push

Offline, private, installable

In two languages

Written down

Get in touch