Cavejam is a free to play remake of Cokemusic. Most of the features that were present in Cokemusic are also present in Cavejam like: Create music with mixer, Play music and gain votes from other players, Building rooms/worlds, Hang out, chat and trade items with friends. Also new features have been added like: Mining ore in the mining world to gain dB's (decibels, ingame currency), Gain rare items through mining, Buying/selling items in marketplace, No limit on building (i.e. rooms can be as large as you like). Signup for free at the homepage. No need for third party extensions. You can directly start playing with any browser.
Video shows how to get started in the game. Also a lot of ingame footage so gives a nice impression of the game.