Myna is a free web-based system for creating music from audio clips.
Start by uploading some of your own clips, or choose from the large free built-in library of vocal, instrumental and rhythm sounds. Then move them around to construct your own sounds. Or if you prefer to just listen to other users' compositions, you can do that too.
So turn your speakers to 11, fire up your browser and head to http://advanced.aviary.com/tools/audio-editor.
If you're not ready to save your work yet, you don't even need to log in or sign up.