Star Wars Shootout is a set of free wargames rules for skirmish combat in the Star Wars universe.
skirmish
Quick Intermediate Level Skirmish
Quick Intermediate Level Skirmish is a set of free wargames rules for battles with small force sizes. It is multi-genre and designed to be simple.
Wild West Skirmish Rules
Steve Burt offers a set of free wargames rules for Wild West Skirmishes.
Fast and Dirty Sci Fi Rules
Looking for an alternative to Warhammer 40K? Who isn’t? This may be it. Even better: these wargames rules are free. Ivan Sorensen’s Fast and Dirty rules also would work for modern combat.
Combat Narrative Fantasy / Medieval Skirmish System
Combat is a set of free wargames rules for playing out medieval and fantasy skimish battles. The author writes:
This is a fantasy/medieval skirmish combat system that is intended to work for narrative style games where there are heroes fighting anything from rank and file minions to Cave Trolls and also where the dramatic action follows some characters more than others. Time is not spread evenly across the tabletop. If Aragorn is running to try to rescue the Hobbits, the heroic character will keep trying to activate Aragorn while the villainous player will keep trying to activate the Orcs fighting Boromir. As part of this, when groups of characters are activated, that is when they get attacked. You cannot be damaged, for example, until the story is talking about you so by activating a group of characters, the player chooses to risk their safety.