UPDATE: 24 hours is up. Hope you got it! If you didn't or even if you did, I still recommend the Hardcover Rulebook, its a gosh darn thing of beauty! Also make sure to check out any HEX games at upcoming conventions!
Hollow Earth Expedition (HEX), one of my absolute favorite RPG rulesets, is celebrating its 10th anniversary today! In honor of that, they're releasing the pdf of their main (extremely fun-to-read) rulebook for free for the next 24 hours! Get it! Get it quick!
If you've never checked out HEX before, you are in for a real treat!