Fanatical is giving away free Steam keys for Ultimate Zombie Defense! To grab your key you just need to subscribe to the Fanatical Email Newsletter. Ultimate Zombie Defense is a Top-down Co-op Survival game with base building and a solo game mode for offline play.
EDIT: Please note this giveaway may not work in some countries.
1. Login into your Fanatical account and subscribe to their newsletter
2. Link a valid Steam account and unlock your Steam key!
3. Launch the Steam client and click the Games menu option.
4. Choose "activate a Product on Steam" to redeem your Steam key.