Highest-quality GIF encoder based on pngquant.

gifski converts video frames to GIF animations using pngquant's fancy features
for efficient cross-frame palettes and temporal dithering.
It produces animated GIFs that use thousands of colors per frame.

It's a CLI tool, but it can also be compiled as a C library for seamless use in
other apps.
gifski is a command-line tool. There is no GUI for Windows or Linux (there is
one for macOS).