I bet it's the Dharma Initiative, Widmore & Hawking.
We also know that Hawking is in fact running a Dharma station and that Widmore is a zillionaire. I'm willing to bet that after The Incident, Jacob told them to leave the island and do what we've seen during the past 5 seasons.
We know the Dharma Initiative on the island was gassed and killed, but what about the ones back in Ann Arbor? I'm willing to bet there are the hard core Razinsky-types, who won't tolerate dealing with the Hostiles... and there are the Chang-types who are willing to work with zillionaire Widmore and Hawking (who was the leader of the Hostiles at the time). We all know what happened to the Razinksy-types (either gassed or left pushing the button), but I'm willing to bet that the off-island DI was willing to cut a deal with Widmore when he showed up post-purge.