fsound is a tool for making (at the moment) one-channel music on microsoft windows

it takes specially formatted text files (*.fss for posterity) as input and spits out 8-bit wav files.

download/read the changelog here:
https://sites.google.com/site/splonglewongle/fsound

shiru also has a flash version at 
http://shiru.untergrund.net/temp1/flsound.swf
but it maybe slightly behind on features.

the original version, for ms-dos/16/32-bit windows (plays sound on PC speaker) has less features, but if you want it you can get it here (songs will still work in the windows version): https://sites.google.com/site/splonglewongle/fsound%28dos%29.zip

fsound has a single channel which can play either white noise or a square wave in seven octaves

if you want fsound on a non-windows OS (linux, mac, bsd, whatever) ask ant1 and it can probably happen