Sound FX soft synth.
Samples on Freesound:
dssi version (Haven't tried it yet):
(Sometimes crash. Just refresh the page...)
I recommend bfxr http://www.bfxr.net/
It should be pointed out that the purpose of this project originally was to give game developers no excuse to not have sounds in their Ludum Dare game jam games.
bfxr is better. More functions and less bugs. I'm frequently stuck with older hardware though and bfxr use adobe air which I can't install.