Snap It! for Mac

From French Touch:

Snap it! is the definitive screen capture tool for MacOS. Contrary to other screen capture tools available, Snap It! is a very low-level screen hacker: Snap It! can take a picture of every part of the screen absolutely whenever you want and save the result in a standard PICT file.
No more troubles in taking screenshots of programs like games which do not give processing time to the Finder or to the classical screen capture programs and prevent them from capturing the screen content.
Snap It! can capture in any bitdepth and in any size provided enough memory is available.