<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.

#include <stdio.h>
int main(){printf("\e[1m");int a,c=0;b:a=getchar();if(a==EOF)return 0;if(!(a&128)||(a&64))printf("\e[%dm","\37! $\"#"[c]),c=c+1-6*(c>4);putchar(a);goto b;}