Gamma World
A strange post-nuclear-apocalypse sci-fi game where mutants (both human and animal) and ultra-tech gadgets abound. It uses a system similar to AD&D¸ with 1d20 roll under a chart result for combat¸ and percentile rolls against attribute*factor. Character creation is random-roll attributes and mutations (there are no skills). The 3rd edition used an unrelated set of mechanics¸ similar to Marvel Superheroes¸ but this was abandoned for 4th edition. A Gamma World supplement was later published for the Alternity system. In 2010¸ a standalone game was published using the 4th edition Dungeons & Dragons rules¸ entitled the ""D&D Gamma World Roleplaying Game."" - A description from https://darkshire.net/jhkim/rpg/encyclopedia/ with kind permission of John H. Kim"