I'll start off:
The Gimp - Someone, can't remember who, keeps plugging this whenever anyone asks about image manip, so you've probably all already heard of it, but I'm including it for the sake of completeness. It's, put simply, photoshop for free, with a nonstandard UI.
Blender - 3D Modelling/animation/rendering suite; it's very good, if a bit hard to learn.
Gaim - Multi-protocol IM client. Does AIM, YIM, Jabber (google talk and compatible), MSNIM, and probably a few others I don't know about.
Ethereal - Network traffic sniffer; good for finding out what's actually going on on your network; has any number of applications, but is most useful for security monitoring. Find out exactly what your computer is actually sending to the 'net!
Terragen - Realistic terrain generator; very tweakable, and very realistic.
That's all I've got off the top of my head. So what do you all pass the time with when your net's down and you're out of books?





