Tiny Wars Fantasy Skirmish is a set of free wargames rules for 15mm figures on a small tabletop.
Featherstone’s Ghost Legions is a set of free wargames rules for using historical figures to fight battles between the dead in the underworld.
The Jackson Gamers present their Medieval version of the venerable Rules by Ral.
Here’s a free, printable pdf of the core spellbook for Frostgrave
Mantic’s Kings of War, Second Edition is now available as a free download. There are also several free Army Books.
I can’t help but thinking that this game is the successor to Warhammer Fantasy, which Games Workshop has essentially abandoned.