The Hot Lead and Steel Sinews Yahoo group focuses on pulp-era gaming. There are also a set of playtest rules for the period, called “Noir.” Unlike other adventure-miniatures games, this set of free wargames rules is specifically focuses on the period, featuring such things as “hero points” to capture the flavor of the pulp novels.
Rugged Adventures, by Kurt Hummitzsch & Robert Murch is a set of free wargames rules written to support Murch’s line of Pulp Figures. These rules have a strong cinematic element, and players are expected to “contribute to the story development.”
Dadie Piombo has a set of basic rules for playing Pulp Action miniatures games.
Cars! is a set of free wargames rules for auto combat.
Pulp Friction is a set of free wargames rules for pulp-style skirmish games. They currently are in playtesting and look very nice.