The Cauldron is a fan-created expansion for the popular (and very good) commercial game, Sentinels of the Multiverse.
Justice League Unlimited Adventures is a build-you-own card game where players try to complete missions while opposed by villains.
Marvel Civil War Skirmish is a miniatures-and-cards game based on the airport battle in Captain America: Civil War. It is played on a checkers or other 8×8 board.
Knight Models offers its Marvel Universe Rulebook free for the downloading.
Godlike – Open Source Rules is a conversion of the WWII Superhero RPG to the familiar d20 type system.