State of Decay will be coming before the end of 2013 to PC. The Steam Early Access version will only support a gamepad, but when it officially launches, it will include keyboard/mouse support.
The game will be unchanged in terms of content, but will sport hi-res textures and a high frame rate. There will be no mod tools released at first, however.
Meanwhile, Update 3 is coming to the Xbox Live Arcade version and will allow players to have an NPC friend join on missions, while a sandbox is being teased as well. No details yet, but the sandbox mode will allow players to build their community and exterminate zombies, and then take some of that community and clean out another valley - which is the same map, but harder and with more zombies.
Undead Labs promises the Update 3 notes will be released later this week.