TAKSI (Windows) - free open source video capture/screen capture software. It allows to take screenshots and record video clips of your favourite games and other 3D-graphics applications. 
Main features:
- Taksi can support live video compression with any VFW video codec your system has installed (i.e. XVid, DivX, MS Mpeg4, etc). 
 - Supports user-specified key mapping, allowing user to assign almost any key to a particular function (such as video start/stop, screenshot trigger, etc.). 
 - Custom video settings are supported 
Basically, this allows a user to specify on a per-game basis the frame rate of the captured video, and the weight of each source frame. The weight determines whether a particular frame is captured or not. This allows for creation of smoother and faster videos, when generic algorithm doesn't produce desired results. - DirectX 8, DirectX 9, OpenGL and GDI based applications are supported.
 - Video can be recorded at either full-size, or half-size in each dimension (using bilinear minification filter).
 - Audio is NOT captured.
 - There is no imposed limit on the duration of the video, only available disk space is your limit.
 - Screenshot file format: PNG or 24-bit BMP
 - Video file format: compressed or uncompressed AVI using any VFW codecs
 
Supported OS: Win95/98/ME, WinNT4.0/2K/XP. 
Latest stable version is 0.7.6 (from June.22, 2006)