Songlio - Free musical guessing game: race friends to name that tune
EarMaster - Professional software for ear training and practical music theory on Windows and Mac.
SongTrivia2.io - Songtrivia2.io is a browser and mobile blind test game that allows you to play in real time with your friends or against strangers. Several musical themes, difficulty and game modes are available to create lots of different musical quizzes.
GitHub Audio - Tracks events across GitHub to generate calming work music
Fretello Stage - Jam, record and share your music in the blink of an eye
GNU Solfege - GNU Solfege is free music education software.