Two Flags One Nation are a set of rules for do-it-yourself American Civil War board games. The author explains how he generates maps and block pieces with his computer.
The Miniature Wargaming Editor
One Brain Cell Vietnam Rules
One Brain Cell Vietnam Rules are a set of free wargames rules for games set in the Vietnam War. They are designed to be a simple, beer-and-pretzels set.
Making Modular 2D Dungeon Tiles
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.