Bunnylin's Chromaticity Compressor
Now available at gitlab!
This free and open-source program takes an image with lots of different colors, and momentarily returns the image with far fewer colors, but still looking almost as good.
The code is kind of a mess, since I wrote it about 10 years ago, but the program still works fine and produces good-quality results.
Main site: mooncore.eu/buncomp
Target: Free Pascal, for win32 only.
Depends: mccommon and mcgloder from moonlibs