Alan Saunders offers Struggle Against Everything And Everybody, a set of free wargames rules for the Mexican Revolution of 1910 – 1920.
rules
Munera Sine Missione Gladiator Rules
Munera Sine Missione is a set of free wargames rules for gladiatorial combat. Author Alan Saunders writes that these are:
Gladiatorial combat rules, using a hex grid. Simple armour and weapon categories make it easy to use your favourite figures, whilst a single bout plays to a conclusion in less than 15 minutes, making it suitable for campaign play in an evening.
Spandau and Lewis WWI Dogfighting Game
Spandau and Lewis is a set of free wargames rules for WWI aerial dogfighting.
Mobile Frame Zero Lego Rules
Mobile Frame Zero is a set of free wargames rules (although you can pay, too, if you like it and can get a printed version) for playing games using Lego and other construction toys. It is very well done.
Earth Expects Space Combat Rules
Earth Expects is a set of free wargames rules for space combat. The authors write:
Earth Expects is a highly detailed set of tactical space combat rules which emphasise skill over firepower. It is well suited to playing battles from duels to squadron actions; because of the high level of detail large fleet battles can be slow to play and therefore optional rules are provided to speed play in these games.