Something I've stumbled across recently is the nice little social music tool Jam With Chrome. It's like a web-based Guitar Band with lots of different instruments including guitars, basses, synthesisers, drum kits and drum machines - including nice clones of the Roland TR 800 and 909 and Linndrumm - and a useable classic and Wurlitzer/Rhodes electric piano. Each is pretty straightforward to use, using an "easy" or "pro" mode for each so that you can control the instrument with mouse and preset chords or go full on with playing with your desktop keyboard. I'm used to using Keyjam with Madtracker so this is nothing new to me and while it's a shame that it doesn't recognise USB keyboards, it's not really that developed that it is going to rival any professional suite any time soon.
The general idea is to get you and three friends (presumably through Google Plus) to share a session together and have a bit of a jam, making up music as you go with the various instruments and tweaking filters, delays, bitcrushers and the like to make sounds. There's a metronome feature to keep everyone in time and it's a hell of a lot of fun though and I encourage people to take a look and use it - if anything it will show Google that we are interested and want to see it developed further!
So what are you waiting for? Get jamming!