I have This is Not a Test by Worlds End Publishing. The physical book is quite pricey, but can be got from North Star Figures. The .pdf is good value.
TnT is a post-apocalypse game and is very good. Its almost a mix of Fallout and Necromunda. You create gangs from various types, buy armour, hand weapons, big guns and go kill the opponents guys. It has a nice way that it deals with turn order/initiative.I like how it plays especially the campaign. You get that similar leveling up as Necromunda with skills and things.
With a bit of work on the background you could change it to any kind of world you want.
This is not a Test has some “Lets Play” on youtube. My favourite being https://youtu.be/w3pO7X8SLeE by Guerrilla Miniature Games, it’s difficult not to get caught up in their enthusiasm!