One of my favourite games during the 80’s was Aftermath!, the post-apocalypse game by Fantasy Games Unlimited. A highly flexible rule system that could be used for gritty, post-nuclear campaigns to quick zombie filled scenarios based on Dawn of the Dead. I loved the game system and it is the only system where I have literally warn-out a set of rules and had to buy another one.
Aftermath! has long been out of print but Amazon have some copies available via 3rd dealers. Check out our RPG store’s Aftermath! page for details. I’ve used it to complete my collection of scenarios as not all of them made it over to the UK.