In 2011, Annie and I participated in a Music Hack Day event in Montreal.
There, we toyed with the idea of making an Android game that uses a MIDI file for a song. Each player uses their song and plays it in synchrony but only the instrument assigned to the player. (We went as far as learning the internals of the MIDI files and finding suitable Java libraries to use but overall this game is still in the idea realm.
The players have to shake their phones following the beat. If they miss beats, they instrument goes silent for a little bit.
It is a silly game but it can be fun to play in a group, generating a Kum Bah Yah moment.