Railgun 2000 is a set of free wargames rules for science fiction armored combat. You need the Fistful of TOWs rules to play.
rules
Armour Battles WWII Rules
Armour Battles is a set of free wargames rules for playing out World War II tank battles. The author writes:
Armour Battles is an introductory set of World War Two wargame rules. Based on the larger Combat HQ rules, Armour Battles is a fully playable game.
Armour Battles features three armoured battles set in Lorraine, France in 1944 as Patton’s 3rd Army advances towards the Rhine. The first battle is a small meeting engagement between US and German tanks. The next battle has the Americans attacking the Germans. This is followed by the Americans attempting to break through the German positions as the Germans counter-attack with a Tiger I platoon.
Armour Battles includes all the rules needed to play these battles.
Note that you will need to surrender an email address for a mailing list to get the rules, but I think you could always unsubscribe later.
Empires of the Seas Age of Sail Rules
Empires of the Seas is a set of rules for the Age of Fighting Sail. The author says that the rules allow battles between large fleets without lots of record keeping.
Tercios Brevis Editio
Tercios Brevis Editio is a free version of the Tercios rules for the Thirty Years War.
Napoleonic Wars Rules
Natholeon’s Empires offers a set of free wargames rules for the Napoleonic Wars.