My playgroup is looking to start a new, stand alone campaign (not long-time running, just a couple of sessions) that is set in a post-apocalyptic world.
We have two distinct sets of criteria. The first is game needs.
It should be able to handle "scaling" easily; i.e., players should be able to control a single character, a group of characters, and a whole clan with relative ease. Preferably, players should be able to control a single character and a group of characters at the same time. Example: Player A controls character Johnnie who is searching for petrol at a decrepit station while simultaneously controlling Patrol Group A who is trying to lead a pack of mutant ravagers away from Johnnie.
It should have mechanics for large-scale travel in groups — something that simulates the hardships of ~300 people travelling the wastes with few resources. Think the band of humans in Banner Saga, but on a bigger scale.
It would be nice if the default setting was post-apocalyptic, but barring that, having a system that easily translates into the setting desired.
The second set of criteria is games that it cannot be. We are trying to play a new game system, one we have never seen before. To that end, this game cannot be:
A d20 variant (d20 Modern, Future, et. al.)
A D&D variant
A Fate variant
A Call of Cthulhu variant
A World of Darkness variant