Trenched is a set of free wargames rules for squad level combat. In spite of the name, it is not a WWI rules set. The example photos are of Warzone science fiction figures.
Rules: Science Fiction
Shock Force Starship Troopers
Shock Force Starship Troopers modifies the Shock Force rules by Demonblade for the Starship Troopers film universe.
Tabletop Titans Super Hero Game
Tabletop Titans is a set of free wargames rules for superhero miniatures games.
Boonta Eve Classic Podracing Rules
Boonta Eve Classic is a set of free wargmes rules for pod racing in the Star Wars Universe. The rules are designed for use with those old Galoob Micromachines, which can still be had for a reasonable price on Ebay:
Away Team Astro Miniatures Skirmish Game
Away Team is a set of free wargames rules for a Star Trek-style landing party expeditions.
There’s also a set of 15mm not-Star Trek miniatures.