The Wrath of Zombies blog has a set of free RPG rules for Mass Combat. While written for the author’s own Thundarr style game, they are applicable to a wide variety of rules and settings.
Rob Conely of A Bat In The Attic blog has written a document on making a Fantasy Sandbox.
Creating a fantasy world? Running a medieval fantasy RPG? Here’s a great article on Medieval Demographics, based on the Paris tax lists of 1292 and other original sources.
Tales of the Grotesque and Dungeonesque offers a Gothic Fantasy Adventure Generator, which produces sentences for adventure seeds.
Morgalad is a fantasy RPG set in a pre-medieval world. You can download the starter set for free.