Steam News announces that The War Z is now once again available for purchase on Steam, following issues that caused them to stop selling the game "prematurely" late last year. They also state this means they are no longer providing refunds to customers dissatisfied with the initial release:

The War Z is now available for purchase on Steam. Valve and Hammerpoint Interactive collaborated to address community feedback, update the Steam store page, and make the title available for purchase worldwide. In addition, a patch has been released to update existing customers. As such, the special refund offering extended for The War Z Steam customers who previously purchased the title has concluded.