<b_jonas> slashlearn euclid//Euclid is a short geeky game in which the goal is to do Euclidean compass and straightedge constructions in as few steps as possible. It runs in the browser, found at "http://www.euclidthegame.com/". It was popular among #esoteric regulars in 2016-07.

zzo38's Farbfeld utilities is a package of command-line programs (with rather strange command-line syntax) for manipulating images in a specific raw format called farbfeld. It's somewhat underdocumented. http://zzo38computer.org/fossil/farbfeld.ui/home