Sand Pebbles Boxer Rebellion Edition is a set of free wargames rules from Bill Molyneaux.
Battle for The Bliss Farm ACW Rules
Battle for the Bliss Farm is a scenario and set of free wargames rules for the American Civil War.
Gettysburg Gamers’ Napoleonic Rules
Gettysburg Gamers offer a set of free wargames rules for Napoleonic warfare.
Thermopylae Free Print and Play Game
Thermopylae is a free print and play solo game.
The Historical Age of Arthur
The Dark Age Wargaming Blog has a nice (long) article (in multiple parts) on the historical Age of Arthur. Doing an historical Arthur skirmish game has been one of my longtime goals.