Linthesia is a game. A game of playing music! You only need a MIDI file to play, and a MIDI keyboard (or your PC keyboard). It's a fork of Synthesia, which only runs on Windows and OS X. Linthesia is for GNU/Linux.
Free music toolkit with 4 million downloads. All-in-one metronome/tuner/recorder. Tuner & Metronome is the best free app for musicians. A professional handsfree metronome and the most accurate chromatic tuner app.
Quaver is a community-driven and open-source competitive rhythm game with two game modes and online leaderboards. Create your own maps or challenge the world in online multiplayer matches.