Avisynth is a scripting language and a collection of filters for simple (and not so simple!) non-linear video editing tasks. It frameserves video to applications.

TortoiseCVS is an extension for Microsoft Windows Explorer that makes using CVS fun and easy. Features include: coloured icons, tight integration with SSH, and context-menu interactivity.

JUnit is a simple framework for writing and running automated tests. As a political gesture, it celebrates programmers testing their own software.

The Saxon XSLT and XQuery processor, developed by Michael Kay

Maxima is a fairly complete computer algebra system written in lisp with an emphasis on symbolic computation. It is based on DOE-MACSYMA and licensed under the GPL. Its abilities include symbolic integration, 3D plotting, and an ODE solver.