Dead Frontier Online
Jagged Blade Software (now Creaky Corpse) made many games with this story in mind, the most recent addition being the MMO "Dead Frontier Online". I'm surprised there is no in-game link to the site, but I see there's one in the summary. People tend not to read summaries, so Imma post a tinyurl here.
http://tinyu rl.com/De FrOnMMO
Just remove the spaces.