Mantic offers a free pdf of their Vanguard Fantasy Rules
The Mainly 28s site has the original Rules By Ral fantasy rules sets.
Axe Age is a set of free wargames rules for miniature wargames in a dark fantasy setting.
No April Fools Here: Osprey is offering the core rules for its popular Frostgrave rules for free this week.
Osprey is offering its basic rules for the popular Frostgrave miniatures game for free.