Dark World War is a set of free wargames rules — actually pay what you want — for playing WWI games that include demonic and mythological creatures.
Assault on Innsmouth is a set of free wargames rules for involving the Lovecraft Mythos. The players are government forces taking on the horrors in Innsmouth. The forces of the mythos are run by the system. The rules are a heavily modified version of the Two Hour Wargames system. There are also expansions at Board Game Geek.
Brimstone is a set of free wargames rules for 15mm to 28mm skirmish battles in Hell. Written by Anreas Udby, the premise is that the Prince of arkness has been slain, and that his lieutenants are battling for control of the underworld. It’s cleverly written, with lines like this:
Panic. There�s also no such thing as morale in Hell. Face it — to have morale, you really need to have such a thing as happiness. In Hell, there are really just shades of panic, hopelessness, and utter despair.
Another part I like is that it turns out that Hell has a caste system and the various denizens won’t always play nice together.
All in all, an imaginative work.
The Jim Bowens Disturbia Yahoo Group has free rules for the Gotterdammerung WWII-Horror game.
Based on DBA, De Bellus Mortuus is a set of free wargames rules for a fun zombie game. Author Chris Brantley writes:
This “just for fun” DBA adaptation is inspired by all those great zombie movies, ranging from the classic Night of the Living Dead to the comedic Sean of the Dead, as well as by the gamers who gather to hack and blast their way through legions of plastic zombies during local conventions. In this game, Players take sides, commanding either the forces of “The Living” or “The Undead.”