Harmonium is, to put it plainly, a musical doodling tool. The user can manipulate notes on a 16x16 grid to create melodies within a pentatonic scale. On top of this already addictive concept, you can bring things to life by enabling Conway's Game of Life!
It's not the easiest thing to explain, so just try it!
It is important to mention, as well, that the concept behind Harmonium isn't my own. André Michelle has a very similar application on his website which served as Harmonium's inspiration.
Changelog
11 June 2009, v1 beta2
Implemented a few features I'd like feedback on before implementing the rest and releasing v1.
New features:
Adjustable tempo
Adjustable volume
2 new GoL modes
Grid shifting
64 grid history
New timing mechanism means even playback
Typematic to make grid shifting and history browsing faster and easier.