Great window manager
StumpWM is really a great window manager. I've tried it, learned some few key-combinations and now i'm really fast doing my daily work, unbelievable. Didn't know anything about tiling-windowmanagers, but now i can't live without this feature. Some applications, like gimp, won't work correctly with tiling but the current git-version has some floating support to handle this (There's also a short intro using gimp with tiling on their website)
An open, cross-platform journaling program.
A scientific plotting package.