Mac Harmonium

Mac Harmonium hides a harmonium inside your MacBook: the laptop lid is the bellows, the keyboard is the keys. Pump air by gently moving the lid — the app reads the lid-angle sensor — then press A S D F G H J to play the sargam notes Sa through Ni. It's polyphonic, so chords stack; notes swell while you pump and fade when you stop, just like the real instrument. No sensor? Drag the bellows on screen with your mouse instead. There's also a free web version at harmonium.lol that reads the same sensor through WebHID in Chrome or Edge, no install needed.

The build story is a love letter to learning by doing. The author is a design engineer for whom real-time audio and hardware sensors were all new, and writes: with Claude, the idea that "lived in my head for years finally had a way out" — "What changed is that now, with Claude, the 'someday' became a weekend." The repo carries a "Vibecoded with Claude" badge and the site footer reads: "Thanks for playing! I built this to learn vibecoding. It's open source."

The sound is genuinely engineered, not a sample: an additive wavetable for the reed timbre, two detuned oscillators per note for the chorused "beat," a tremulant LFO, per-note ADSR envelopes, and a lowpass plus compressor to keep stacked chords warm. It's MIT licensed with five releases, a Homebrew cask, a clean VirusTotal scan, and an honest note about why it isn't notarized yet. Swift and SwiftUI, per the repo badges.