Something like this? https://github.com/tiquthon/onion-or-not-the-onion-drinking-game-2

Some time ago this was also up, but now it isn't: https://github.com/SchaeStewart/OnionOrNot

Basically this search: https://github.com/search?q=onion+not+onion+game&type=repositories&s=updated&o=desc