Unison, the rsync-like tool, has an awesome interface. ( https://www.cis.upenn.edu/~bcpierce/unison/ https://www.cis.upenn.edu/~bcpierce/unison/ ) Prolog. The

Unison, the rsync-like tool, has an awesome interface. ( https://www.cis.upenn.edu/~bcpierce/unison/ https://www.cis.upenn.edu/~bcpierce/unison/ ) Prolog. There's a reason it's been king of the Logical Paradigm for decades. Oberon OS. Turing Drawings. ( https://maximecb.github.io/Turing-Drawings/ https://maximecb.github.io/Turing-Drawings/ ) procmail ( https://en.wikipedia.org/wiki/Procmail https://en.wikipedia.org/wiki/Procmail ) one of the most beautiful (yet hideous) programs I have ever read.