Dear Esther is making the move from the Source Engine to Unity as it readies for release on the consoles. So, why the switch? Apparently there were some hidden costs associated with using the Source Engine that The Chinese Room wasn't aware of initially.

Robert Briscoe explains how he received a "huge bill" for some of the middleware included in the Source Engine. He says that neither he nor his team was aware of any of the middleware of the fees associated with it. The team also had to p ay for separate license for each platform and resulted in "a big hit financially."
"This was all happening around the time of the departures at Valve, which unfortunately included our main contact for all things Engine related, and subsequently we spent weeks trying to find someone else who could point us in the right direction," he says. "This had a cascade effect on the whole project, leading to months of delays; coupled with the contractor's inexperience with the engine, communication problems, and then finally the PS4 release date announcement, we decided it was time to pull the plug, at significant cost to us.

"We also got the underlying impression that official engine support was not long for this world, making me all the more anxious, not just about the possibility of further ports, but about the future of Dear Esther in the years to come."

It was then that he decided to make the jump to Unity. With the help of the Playmaker and Shader Forge plugins, Dear Esther is now in the process of going from Source to Unity.

A beta for Humble Bundle and Humble Store consumers may get to test out the Unity release prior to receiving a full release. You can read a great deal more from Briscoe over at LittleLostPoly.