Coastal Command is a set of free wargames rules for small coastal craft in World War II.
naval
Nauta Ancient Naval Wargame Rules
Nauta is a set of free miniature wargames rules for playing out ancient naval battles. The files are hosted here:
La Felicissima Armada Naval Rules
Jim Wallman offers a set of free naval wargames rules called La Felicissima Armada. It’s a Spanish Armada naval game designed to use 1/144 plastic ships on the floor.
Battle of Jutland Quick Play Rules
Matt Fritz has written a set of quick play rules called Day of the Dreadnaughts for recreating the Battle of Jutland. The set includes links to paper models, in case you want to try it, but don’t hvae the appropriate miniatures.
Design and Fight A Civil War Ironclad
Pete Pellegrino has written a set of free miniature wargames rules called Damn The Torpedos. In the game, you customize your ironclad, and then take it out to fight in the Cvil War battle of Mobile Bay.