Thanks to -FUPPETS- friend STEVOK from the Sonic Youth Gossip Forum for this link.
There have been several webpages where you could make a tune or create a song, but the iNudge page is simply the best yet. Not only can you change instrumentation, but you can extend the measures as long as you need, giving you the opportunity to write longer, more complex beats and pieces of music.
Check it out, explore the possibilities, and if you like, post a link to your finished piece in the comments section!
Here are just a few examples, made by the SY fantatics. Click on their screen names to hear the tunes.
STEVEOK - ANTAGON - BRELIGION - BEAUTIFUL PLATEAU - ANN ASHTRAY