Dan Brown offers A l’Ombe des Aigles, a set of free miniatures wargaming rules for Napoleonics miniatures.
I stopped buying Warhammer 40K stuff when they dropped the squats as a major race. In my basement workshop, I’ve got a horde of the stunties, in regular battle gear, on trikes, in exo-armor … you name it. You can find an online squat codex in the War Vault.
Matakishi has written The Natives Are Restless Tonight, a set of free wargaming siege rules for any game involving a large band of natives, and a small, but stalwart group of westerners. They would work for any game in the colonial era, including the Zulu War, Boxer Rebellion, Foreign Legion, North West Frontier and Indian Mutiny.
The rules use a card activation system, and involve rolling handfulls d6s. Casualties are determined by summing the attack dice and removing a figure for every multiple of 6, 9 or 12, depending upon the defensive situation.
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.
Here’s a page with some errata and clarifications for Warhammer Ancients’ Alexander The Great book.