Carbine Studios, its latest developer. According to the press release, Carbine has some very apt cogs in its machinery deriving from 17 former Blizzard employees, "including lead and senior developers from the World of Warcraft team," including lead designer Kevin Beardslee, who is now the vice president of design.
Additionally, former Fallout designer Tim Cain has been tapped to be the programmer director. Carbine is currently working on an unannounced MMO, according to their website. No other details have been revealed, but the team definitely has a powerhouse of employees.