Steve Burt offers a set of Napoleonic Wargames rules.
Burrows and Badgers Rules
Burrows and Badgers is a set of free wargames rules for tabletop adventures with bands of anthropomorphic animals. There’s also a supporting set of miniatures.
Fields of Battle Fantasy Rules
If you have an account with Scribd, you may be interested in a set of fantasy rules that appeared in Warlock Magazine in 1986: Fields of Battle by Graeme Davis
Free Military and Historical Ebooks
Feedbooks has a list of some fifty free military and historical books.
Renaissance Naval Rules
David Heading offers a set of Renaissance Naval Rules.