I've been contributing to a project called Folk computer[1]. It's focused on creating a physical medium for computing (think printing out a program, which is then tracked by the computer. There's some really cool spatial interaction that happens). Folk v2 is currently in development, so I've been digging into the guts of the datalog-like engine. It's been a lot of fun to pick up C and see it applied to a project I can directly interact with!

[1] https://folk.computer/