The original source is very old. Written in plain TeX. Most source files in the TUG TeX Showcase archive [1] are dated 1998. Undoubtedly the first versions were

The original source is very old. Written in plain TeX. Most source files in the TUG TeX Showcase archive [1] are dated 1998. Undoubtedly the first versions were much earlier. As the TeX Showcase master page [2] notes, the author was Steve Seiden, from LSU. He died in a bike accident in 2002. [1] https://www.tug.org/texshowcase/cheat-20131114.tar.gz https://www.tug.org/texshowcase/cheat-20131114.tar.gz [2] https://www.tug.org/texshowcase/ https://www.tug.org/texshowcase/