The Jackson Gamers offer Ancients By Ral, an ancients version of the venerable Rules By Ral system.
Miniatures Rules
Angels 1-5 World War II Air Combat Game
Angels 1-5 is a game of air combat over Britain in 1940
Star Breach Sci Fi Rules
Star Breach is a set of science fiction rules that are miniatures agnostic. The free 1st edition core rules are available at the link. There’s also a deluxe version you can buy.
Wild In The Streets Rules
Wild In The Streets is a set of free wargames rules for battles between youth subcultures in the streets. Interestingly, the setup is designed so that the game begins when the fight has already started. That keeps players from wasting half the night getting into the action.
Planet 28 Sci Fi Skirmish Rules
Planet 28 is a set of free wargames rules for “quick narrative games between warbands of warriors, mutants, and outcasts.”