The second edition Maifaux Rules are available free for the downloading.
Colonials vs Martians is a set of free wargames rules for steampunk adventure. The author writes:
The great behemoth landships with coal fires stoked and steam boilers at full pressure chub their mighty pistons, sending vibrations of fear shaking the ground and hearts of men. Landships are the tanks of H. G. Wells imagination and the main figures in this game, One per side along with 4 (5-10) man infantry squads, gatling gun, and a cannon crew of two men, or limits of your imagination… as you experiment with more squads and/or landships in larger battles. The enemy of our Victorian Era heroes armed with steam and black powder? Martians! These are Martian’s not of -war of the worlds- level tech, but who grasp ‘like’ ability weapons they may have a co2 powered bolt weapon or Martian water pistols (to be cool) but just use “musket” stats. How they got to earth in the days of the Victorian colonial era or we got to Mars… um, would you believe natural space worm portholes? How about Martian Either water, that negates gravity, painted on wooden sailing ships? That wacky Ether!
James Clay has written a fine article on wargaming in the world of the Difference Engine.
For those who don’t know, The Difference Engine is a novel by William Gibson and Bruce Sterling that takes the reader to a Victorian world in which Charles Babbage’s Difference Engine drives cybernetic steam engines. While I did not enjoy it as much as Gibson’s Neuromancer, it still was a good read.