Colts and Arrows is a set of free wargames rules for wild west skirmishes.
Miniatures Rules
Lion of the North Thirty Years War Rules
Lion of the North is a set of free wargames rules for battles set in the Thirty Years War. The rules set also includes Haiduk and Rajtar for period battles in Eastern Europe, and a set of army lists.
Maurice Lite Rules for the 18th Century
Maurice Lite is a sampler version of Sam Mustapha’s rules for warfare in the 18th Century.
Strange Aeons Eldrich Horror Skirmish Game
Set in the pulp 1920s, Strange Aeons is a skirmish game that sets bands of adventurers against Lovecraftian horrors. The game is commercial, but they have a free test version.
Roma Victa “Pulp” Rules For Ancients
If you scroll down on the Lead Adventure thread at the link, you will find a simple set of free wargames rules and a skirmish scenario for Late Roman “Pulp” Adventure.