1450 – 1550 is a set of free wargames rules for playing miniature games set in the renaissance. The author says it’s “slightly more complicated than Tactica.”
Into Glory Ride is a set of free wargames rules for battles set in the Renaissance and beyond. It covers the era 1500 – 1900.
Arquebusier is a set of free wargames rules for skirmish games set in the Renaissance.
The Krigsspil site has a huge number of medieval and renaissance flags available for downloading.