"slot machine" was a hardware task in the reverse-engineering category on Google CTF Finals 2017, which took place in Zurich back in October 2017.
All teams got the same ATtiny-based slot machine game, which contained 2 stub flags. The objective was to reverse-engineer it by disassembling it (in literal real-life sense) and dumping the firmware, figure out how flags can be obtained without access to the circuit, and do that with the machine at the organizers' table, which contained the real flags.
You can read the rest [here](https://blog.bushwhackers.ru/slot-machine-write-up-google-ctf-2017-finals/)