If you want to grab yourself a free copy of reverse tower defence game Anomaly: Warzone Earth, here's what you need to do. Head over to Bundle Stars' Facebook page and follow the instructions to get your code. Nice and simple.
They've got 100,000 copies of the game (PC, Mac and Linux) to give away, but seeing as they're free it's probably best to get in early to avoid disappointment. Bundle Stars regularly release bundles of indie games on their website, you can their latest offerings here.