Any RPG the Game Master preps to run for only 2 hours at a time.
I know many people will dip to the quick and easy answer of Fiasco.
The reason for this is many people are of the opinion that there are not many RPG systems out there that fit well into a 2-hour time format. This because traditional games like D&D or Pathfinder are slogged down with heavy time killing combat rounds. But with some creativity and proper planning, even these games can fit into a 2-hour format.
While Fiasco is a good go too for many reasons I think that as long as your players show up ready to play and with a little planning on the GMs part any RPG can fit fine in a 2-hour format. Simple tricks
Simple tricks that a DM can use like minion monsters and Hit Points capped at half-HP for monsters can still keep games interesting but speed up combat rounds considerably. Allowing you to get to the end of a session and face boss monsters with time to spare.