My personal #hangoutshackathon project "Hangout Band" is coming along nicely, now also featuring a piano synced with all participants in addition to the drums.

All graphics created with CSS3.
Audio via the Web Audio API.
Synced with others via Google+ Hangouts sendMessage/onMessageReceived mechanism, which is amazingly fast.

Until the sendMessage functionality is available outside of dev-hangouts you can try the stand-alone version here:

(Probably only works properly in Chrome...)
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