Wes Rogers offers set of free wargames rules called Feudal Warfare, described as a “fairly simple set” of convention rules.
Rules: Medieval
War of the Red and White Wars of the Roses Rules
War of the Red and White is a set of free wargames rules for multiplayer Wars of the Roses Games.
Blood, Guts and Rampant Hex Medieval/Fantasy Rules
Blood, Guts and Rampant Hex is a set of free wargames rules for “beer and pretzels” games in a Medieval/Fantasy setting.
My Kingdom For A Horse Wars of the Roses Rules
My Kingdom For A Horse is a set of free wargames rules for playing games set in the medieval and Wars of the Roses period.
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.