Amazon offers a free kindle edition My War at Sea 1914–1916: A Captain’s Life with the Royal Navy during the First World War
The Miniature Wargaming Editor
Babylon 5 Fleet Book For Full Thrust
Here’s a Full Thrust fleet book for the ships of Babylon 5. Obviously, you’ll need to have a copy of Full Thrust.
Starship Trooper Rules
Kurt Bowker has written a set of free wargames rules set in the Starship Troopers movie universe. I’m not sure where you would get the miniatures to go with these — perhaps Ground Zero Games has something that could be used.
Dungeon Squad: Adventures in the 41st Millennium
Dungeon Squad: Adventures in the 41st Millennium is a RPG set in the 40K universe.
Jeu Des Battailles
Jeu De Battailles is a set of free wargames rules for battles during the horse and musket era.