Founder's Packs are a way to support the developers of Dauntless (Phoenix Labs) and get a few bonuses before the game releases.
The Founder's Packs are split into 3 tiers, higher tiers include the content of the lower ones. "Whether you’re looking to become part of Dauntless history, get a jump-start on customizing your character, or are looking for early access, we’ve got something for you." -Phoenix Labs
The packs have been available for purchase since april 4th 2017.
