Get Warhammer 40,000: Rites of War for free from GOG.com. Free for the next 34 hours.
And if you feel like donning Space Marine Terminator amour and smashing hordes of Tyranids in a first-person shooter, check out Space Hulk: Deathwing. Now available DRM-free on GOG. Among other Warhammer 40,000 titles, you can get Space Hulk: Deathwing on sale over the weekend too.