The Red Golem Blog has a tutorial on making modular 2D dungeon tiles.
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.
Resolve Napoleonic Rules
Resolve is a set of free wargames rules for Napoleonic warfare.
Simple Sails Rules
Simple Sails is a set of free wargames rules for Napoleonic fighting sail.
Obydon 40K Rally Rules
Obydon 40K Rally is a set of free wargames rules for combat races using various Warhammer 40K vehicles.