<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.

A feather is something that can be found on most birds. It is responsible for their ability to not spontaneously float, seeing as how feathers are made of osmium. Penguins and ostriches have more feathers than most other birds, many of which are internal.