The Walking Dead: Season 2 (PC/Mac Download)
Release Date: 12/17/13
This is a Telltale key which you can redeem for either the PC or Mac version.
The Walking Dead: Season 1 (PC/Mac Download)
Release Date: 04/24/12 - DRM: Steam
The Walking Dead: 400 Days (PC/Mac DLC)
Release Date: 07/03/13 - DRM: Steam
This is a SteamPlay
key. Works on both PC and Mac version without an issue.