Between 1968 and 1970, wargaming pioneer Charles Grant wrote a serialized wargames guide in Meccano Magazine. The serial is now available as a free download. This serial eventually became his classic Battle: Practical Wargaming.
rules
WWII Platoon Commander
WWII Platoon Commander applies the mechanics of the Blitzkrieg Commander rules to a skirmish system.
War of Spanish Succession Supplement for Black Powder
& Blenheim Palace is an unofficial supplement for the popular Black Powder rules.
Road Cycling Tour Miniatures Game
Fog’s Soldiers offers a set of free miniatures rules for Road Cycling, and not incidentally, a line of miniatures to go with it. You don’t need them, though, because you also can download printable rider tokens.
Jousting Tourney Rules
Al Hewitt and Ric Willey offer Jousting, a set of free wargames rules for medieval tournaments.