To celebrate GOG's six million game downloads, they partnered up with Revolution Studios and are giving away a free copy of Broken Sword: Shadow of the Templars until October 1st. This also includes a free copy of the original version! Both are Windows only.
Check it out. You have to sign up but you'll get a free copy if you "buy" the game so it's added to your library. There's also six other free games here.