Wrath of Kings is a set of demo rules for a fantasy skirmish system. It has some interesting concepts.
fantasy
Dungeon Delver Card Game
Dungeon Delver is a free print and play card game of dungeon exploration.
Fields of War Fantasy Rules
Fields of War is a set of free wargames rules for fantasy armies. In addition to the core rules, there also are a large number of interesting army lists.
WWI Fantasy Rules
Orks and Dwarves in a WWI setting? Sure. Here’s a set of fantasy WWI Rules.