PZ8 Sci Fi is a set of free wargames rules for using 6mm (microarmor) figures in a science fiction setting.
The Miniature Wargaming Editor
PZ8 1950-69 6mm Wargames Miniatures Rules
PZ8 1950-69 is a set of free wargames rules for using 6mm miniatures to refight battles of the mid to late 20th century.
Free Age of Sigmar Rules
Games Workshop offers the core rules for its Age of Sigmar Rules free for the downloading.
Making Eldar Terrain For Warhammer 40K
Ironhands has a page with tips for creating sufficiently alien Eldar terrain for your Warhammer 40K games.