Red Banner is a set of free wargames rules for modern naval combat.
naval
Corvus Ancient Naval Rules
Corvus is a set of free wargames rules for fighting ancient sea battles.
Renaissance Naval Rules
David Heading offers a set of Renaissance Naval Rules.
Togo Russo Japanese Naval War Rules
Togo is a set of free wargames rules for naval battles during the 1904 – 1905 Russo-Japanese war.
Schnell Rules For Schnell Boote!
Schnell Rules is a set of fast play rules for WW2 coastal forces.