SMART stands for Simple Miniature Adventure Rules and Tactics. They’re a set of free wargames rules for fantasy and medieval gaming.
medieval
Medieval Skirmish Rules
Bob Beattie offers a set of Medieval Skirmish Rules.
Internet Medieval Sourcebook
The Internet Medieval Sourcebook is a fantastic resource for miniature wargamers. I’ve had this one in my bookmarks for several years and haven’t even begun to plumb its depths. The section on the Crusades is particularly useful.