The Basic Fantasy Role Playing game is just that — a role playing game released under the Open Game License. it’s based on the d20 3.5 rules, but takes its inspiration from old school role playing.
And One For All
And One For All is a set of free wargames rules from Eureka Miniatures for swashbuckling adventure in the tradition of the Three Musketeers.
Pz8 Wargames Rules
This 24 page pdf has Pz8’s relatively simple free wargames rules for a variety of periods, including
Colonial
WW1 Divisional
WW2
WW2 Divisional
1939 – 1941 Naval
WW2 Coastal
1935 – 1965 Aerial
1965 – 1075 Aerial
1950 – 1975
1975 – 2010
Science Fiction
Space Combat
Raum Krieg
Raum Krieg is set in an alternate history where Germany and the Allies battle it out in the skies with UFO Technology.
Warhammer Skirmish Rules
Here’s a set of rules for converting the large scale Warhammer Fantasy battles game to a skirmish version.