Osprey is offering its basic rules for the popular Frostgrave miniatures game for free.
Here are a set of rules for a tower defense game with miniatures.
The premise, according to the author:
You are the sole defender of a precious Portal which allows travel between worlds. Orcs want to travel to other worlds, because theirs sucks. They will smash down the gates and doggedly pour through the castle into the portal, if you let them. Miniature Tower Defense is a tabletop game inspired by video games such as “Orcs Must Die” and “Sanctum” in which the hero places traps to stop mindless hordes of enemies, while also fighting them personally.
Tom’s Ancient Warfare Rules is a set of free wargames rules for the ancient period.
Labyrintus is a set of free wargames rules in which players try to get their team of miniatures through a labyrinth maze.
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.