<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.

FireFly was a short-running but well-loved sci-fi TV series released in 2003, starring Nathan Fillion and directed and written by Joss Whedon. It's also a room whose gimmick is that it gets darker as you kill the enemies.