It's a community event on steam. If everyone signed up completes 500000 hours of playing in certain stratagem games, per day, they get a free bundle of stuff each day they accomplish it. Usually it's a dlc, an older game and them 75% off something else. The games you can play to contribute are total war Warhammer 1 and 2, company of heroes 2, dawn of war 3 and endless space 2.
It's worth it just to sign up. It's pretty much a guarantee of some free stuff. Yesterday was some game called vikings and the grim and the grave DLC for total war Warhammer.