My primary Operating System since 1996 is GNU/Linux. Most of the software I write in my free time is Free Software for Unix.
Revision control software:
I am an FVWM developer.
I learned the multi-platform graphical library SDL by writting a simple game called VelaTron.
My old DOS programs are available as well.
Currently I hack on my company's projects to compete with Google, well, kind of. :)