Once available as a commercial rules set — and a nice one it was — Knights and Knaves now is available as a download. Also available are the More Knights & Knaves and Castles, Cogs & Chevauches expansions.
medieval
Medieval Siege Rules
Ryan Scow offers a set of free medieval siege rules.
Agincourt Board Game
GMT Games offers a free download of a Battle of Agincourt game. If you’re familiar with their commercial board war games, you’ll know that they have wonderful graphics and gameplay, both of which are on display here.
Medieval Breeches
And now for something completely different. But maybe still useful.
I. Marc Carlson has written an artcle on medieval breeches. Yes, pants. There are a number of illustrations, and this interesting fact: no actual medieval breeches have survived to this day, so no one is really sure how they were constructed.
Still, its a useful resource for sculptors and painters.
Sword and Dagger Medieval Skirmish Rules
“Herkybird” offers a set of medieval skirmish rules based, in part on an older rules set called Retinue.