Britannia Games Ltd, publishers of the mother (and father) of all sim games, Chivalry & Sorcery, have started making PDF products available through drivethrurpg.com. Their particular store is here.
I have a huge soft spot for C&S. It is unashamedly proud of the levels of simulation it aspires to (and usually hits). C&S2’s sourcebook articles on medieval economics are probably responsible for my passion for medieval agriculture. I’ve played games with Ed Simbalist (original C&S co-author) and Steve Turner (Britannia’s primary writer) and other Britannia luminaries.
At the moment, there aren’t any rulebooks on the store. There are some free maps of the Rebirth-era setting, Marakush, with some Marakush setting books. There’s also a scenario by Steve called Treachery, which includes HarnMaster stats and advice on adapting the scenario to a Harn campaign (the latter by me).
While we’re on the subject of C&S PDFs, there’s something masquerading as a reprint of the original C&S knocking around the net, put out by a firm called Gamestuff (set up by the late Wilf Backhaus). Unfortunately, it isn’t the original, nor is it legal. Wilf didn’t own the IP – his one-time writing partner Ed Simbalist and his partners invested quite a lot of money recovering the IP from Fantasy Games Unlimited, the original publishers of C&S.
If you want a 1st edition C&S, scour the firms selling second-hand games. If you’re lucky, you’ll find one (though personally, if you’re looking for an older version of C&S, I find the second edition far more playable).