Andy Watkins offers Hammers Slammers, a set of generic science fiction rules. Watkins has designed a lot of rules, and in each he seems to have created interesting and enjoyable rules sets.
Miniatures Rules
Seas of War WWII Naval Wargames Rules
Stephen Lorenz offers a new set of WWII naval wargames rules called Seas of War. The set is professionally done and presented in pdf format. It also includes the data on a huge number of ships of the period.
North Against South Fastplay Card Rules For the ACW
Rudi Geudens has written a modification of Richard Borg’s Battlecry game for miniatures. You need a set of the original rules to play, though.
Afriborea Colonial Wars Rules
Prolific games designer Rudi Geudens offers Afriboria, a fast play, card driven set of colonial rules. What’s really neat about this game is that Rudi has designed some gorgeous custom cards, as well as labels to stick to six sided dice for use with the game.
Lego Knights
Gurth offers a set of free wargames rules for using those Lego figures that your kids (or maybe you!!) have hidden under the bed.
When my kids go off to college, I’m going to have the biggest collection of Legos any middle-aged man has ever had.