Games Workshop offers the core rules for its Age of Sigmar Rules free for the downloading.
Miniatures Rules
Fleet of Battle Ancient Galleys Wargames Rules
Fleet of Battle is a set of free wargames rules for playing out battles between fleets of ancient galleys. Think Ben Hur. There also are several pages of free print-and-play galleys for use in lieu of lead miniatures. The rules require a knowledge of the commercial Field of Battle wargames rules.
Kampfgruppe Ost WWII Rules
Kampfgrupp OST is a simple Hex based Operational level WWII game circa 1944-1945 East front.
Pacwar Space Dogfighting Rules
Pacwar is a set of rules for large scale dogfights in “The Universe.”
Capitana Wargames Rules For Galley Warfare In The Mediterranean
Ray Lucas offers Capitana, a set of naval rules specifically for 16th Century galley warfare in the Mediterranean. They were written for the NLWG 2009 convention game.