I just realised the most obvious one that we've all forgotton...and it works under *any* operating system. You can even use it without a computer (and that's how it's designed to be used:)
http://unplugged.canterbury.ac.nz Tim Wright Assistant Lecturer Department of Computer Science University of Canterbury "Language, like terrorism, targets civilians and generates fear to effect political change." -- "Collateral Language" John Collins and Ross Glover ed.
