Roc from Aviary is a free online music creator that lets you create music online easily. It comes with lot of instruments that you can choose from. This online music creator has a very easy to use interface using which create your music easily.
Update: (July 08, 2013) The service has been shut down. You can instead check out AudioSauna.
Roc comes with lot of instruments, like different types of drums, percussions, piano, Harp, Guitar, Sitar, Beat box, and many more. You start by choosing an instrument for your music track. After that, you can use various sounds available for that instrument, and then create your track.
Here is a video tutorial that explains how to use Roc:
As you can see, Roc is really easy and fun to use. I tried it for the purpose of this review, and ended up spending lot of time on this addictive music creator. It is so easy and fun.
Roc is a really advanced web application, but it does not needs any download or installation. I am really impressed by prowess of Aviary in creating web applications. Other advanced Aviary application I reviewed earlier includes HTML5 based free online photo editor.
Try Roc free.