••• A newer release with an important bugfix is available •••
To use:
./gifsicle --lossy=80 -o lossy-compressed.gif input.gif
Adjust --lossy argument to suit quality (30 is very light compression, 200 is heavy).
It works best if the input image/anim is high quality and doesn't have heavy dithering (lossy compression will add its own dithering).
Demo
3.3MB original
1.9MB lossy
Big thanks to Nico Bergemann for finding the bug that was stopping this release.