Fighting Fantasy Blog has published a set of “Fighting Fantasy Mass Battle” rules from a 1986 issue of Warlock magazine. Ahhh … such Old School Goodness.
Bob Cordery’s Bundok and Bayonet free colonial wargames rules are available here. They are a clean, well-written set that use a card activation system. Two things I really like about these rules: 1) that you check morale before moving 2) a bucketsful of dice mechanism for combat.