The FL-909 is a Flash-based clone of the famous 80s drum machine, the Roland TR-909. This and other interesting experiments can be found at lab.andre-michelle.com. (Hat tip: rekkerd.org.)
If you really like it, you can install his cross-platform desktop version, which uses Adobe’s new AIR (Adobe Integrated Runtime) technology. Or, you can nab the source code and compile your own. I haven’t tried either yet, mind you.