During his GDC session Bungie lead network engineer David Aldridge confirmed earlier rumors that they are working on a "massively multiplayer action game" with Activision.
Rumors have spread a few weeks ago claiming that the only project currently being developed by Bungie is an MMO titled "Destiny". Aldridge didn't confirm or deny that, but he stressed that the new MMO won't be a World of WarCraft in space.
Bungie has developed and released 6 Halo titles for Microsoft until they parted ways earlier this year. The new game is the first title in a ten year multiplatform publishing deal signed with Activision. The financial terms of the deal were not disclosed, but Bungie has confirmed that it will keep the game's intellectual property rights.