Scavenger Skirmish Survive

Scavenge Skirmish Survive is a set of free wargames rules for a tabletop game set in a post-apocalyptic volcanic winter. Link goes directly to a pdf

Road Warriors rules

Michael Taylor has written Road Warriors, a set of free wargames rules that uses Matchbox cars for games set in a post-apocalyptic future, ala Mad Max.

Urban Warzones Rules

Urban Warzone is a set of free wargames rules for near-future urban combat in a post-apocalypse world.

Wastelands Post Apocalyptic Wargames Rules

The author writes:

Wasteland is a game of post-apocalyptic warfare between small bands of desperate fighters. You can play it as a skirmish war game using the character archetypes and weapon lists but it’s also designed to allow you to play fast-moving and memorable campaigns with two or more players.

Autokill Auto Combat Game

Autokill is a set of free wargames rules for vehicular combat.