LilyPad
LilyPad is (was) a Mac OS X quasi-real-time previewer for the LilyPond music typesetting system. I never got it anywhere close to where I wanted it to be, and I am currently looking for someone to take over its development or replace it with something new.
LilyPad does not work with current versions of LilyPond, so it’s not even slightly useful anymore. If somebody takes it over, I’ll post a link here.
The old LilyPad Page is available here, if you’re interested, and you can see information about the code here.