Colouring Computers: non-electronic computers that work when you colour them according to a simple set of rules.

I find this very cool, it reminds me a lot of the Usborne computer books from the 80s.

https://ipfs.io/ipfs/QmYz7DPRWypGQcbAHr7Mi8EKB6ntSPsEnUsCXbAhBiHQZP/