Tombstone is a free RPG set in the wild west. It’s designed to be rules-light, and has quick play character creation to get you started.
Battlemap: Shrine of the Bronze Dagger is a free fantasy battle map usable with both RPGs and tabletop miniatures. The map shows a shrine, and the living quarters of a dark cult. It occured to me that it would also be great for a Cthulhu mythos adventure using the Pulp Alley games, so I’m going to download it.
Ironsworn is a fantasy RPG that can be played with a traditional GM, as a co-op, or solo game. In this setting, players are heros pursing quests. There is a free downloadable version, as well as commercial soft and hard cover editions.
Taktika is a set of free wargames rules for science fiction battles.
Black Hat, White Hat is a set of free wargames rules for Wild West skirmishes.