Off the top of my head, several roguelikes (e.g. ADOM, Caves of Qud, ToME) and several entries in the TES series (e.g. Daggerfall, Skyrim) support it.

I also remember at some point playing an RPG where you found an ongoing even fight between two armies and you could join one to make the fight go your way, but I don't remember what it was.