Ram or Die is a set of free wargames rules (and paper figures!) for refighting the Battle of Salamis.
Rules: Naval
Seas of Lead WWII Naval Rules
Seas of Lead is a set of free wargames rules for World War II Naval games. Along with the rules are some good looking unit data cards that they made using the Magic Set Editor.
WWII Naval Rules
Here’s a set of very simple WWII Naval Rules.
Destroyer Commander
Destroyer Commander is a variant for Mongoose Games’ Victory At Sea that focuses on smaller ship actions. I have always wanted to do Destroyer and PT Boat games.
Simple Sails Rules
Simple Sails is a set of free wargames rules for Napoleonic fighting sail.