zeit is using "Lisp in 1k lines of C" https://github.com/Robert-van-Engelen/lisp
I'm confused by this. The source code contains a Gauche Scheme file.
Ah yes, there is a tool to select the images and a helper to convert the images for the game. Those are written in gauche scheme. But the game itself is written in the small Lisp.
Thanks for the clarification! The list has been updated.