GHQ has a free pdf of its Beer and Pretzels Modern Micro Armor game, formerly a commercial effort, now a set of free wargames rules.
GHQ has a pdf of its Beer and Pretzels WWII Micro Armor, originally a commerial set, now a set of free wargames rules.
PZ8 WWII is a set of free wargames rules for fighting battles of the Second World War using 6mm (microarmor) wargames miniatures.
Micro Armor Devastation is a set of fast play miniatures rules for land and air combat from World War II onward. They’re very nicely done in a pdf format.
Final Combat Micro Melee is a set of free wargames rules that converts the Final Combat skirmish system for use with Micro Armor.