Krieg Ist Mist is a set of free wargames rule for 6mm games set in WWII.
From Baccus Miniatures comes Gettysburg At The Gallop, a set of free wargames rules for the American Civil War in 6mm.
Legion Wargames has a tutorial on painting 6mm figures.
Legio Wargames offers Legio VI Macedonia, a set of free wargames rules for playing games set in the Helenistic through the Republican Roman eras. They’e designed for 6mm figures, with one 20mm x 20mm stand equaling 300 – 500 heavy infantry.
Legio Wargames offers Legio VI Julia Augusta, a set of free wargames rules for battles of the late Roman Republic and Empire (100BC to AD250). They’re designed for 6mm, where one 20mm x 20mm stand equals a cohort.