A few years ago, I was working for a company that sold, among other things, financial transaction processing machines - debit and credit transactions. We call them EFTPOS machines here in NZ, and I worked on the software that goes inside them.
I believe that I am the first person in the world to program games for an EFTPOS terminal.
I did the work on my own time, but the games were certified and were installed on machines for many years. The games have disappeared from more recent software revisions, so perhaps the current developers needed to reclaim some of that code space; I don't know. It was a gas to show how to access these hidden games, to people working at random points-of-sale.
The terminal had a touch-screen interface. I created five games in all. They would all print their instructions, and most would remember and display your initials and past high scores. When you won, the game would display one of the "fortunes" from the old microsoft "mah-jong" game, I believe (including the very weird "Bouncy ball is the source of all goodness and light").
A 'Concentration' memory game, 20 'cards'.
Doodle (draw images, save them, print them on the receipt paper).
Attaxx (othello-like game, modelled from an internet game I had).
A sliding-tile puzzle game - 15 tiles, where you move the 'hole' around.