Dear Esther run in Unity, rather than Valve's Source Engine, and he has some pretty gifs to show for it. He's bringing the entire game to Unity, six years after it launched as a free Source engine mod and two years after it launched as a separate game, also in Source. In a blog post, Briscoe asks the question on everyone's mind, "Why would you want to port Dear Esther, a fully finished game on a solid engine, over to an entirely new engine so late after release?"
Thankfully, he also answers the question, with a bit of background information: Briscoe, thechineseroom's Dan Pinchbeck and Jessica Curry, and coder Jack Morgan made the 2012 PC launch game, and then the team split to work on their own things (Amnesia, anyone?). Briscoe outsourced the Mac and Linux ports of Dear Esther to two separate teams, which have since dissolved and stopped bug-fixing those versions. Another, native Linux port, is still in beta and looks like it's staying that way.
Briscoe received a "huge bill" for the middleware included in Source Engine but not covered in the original licensing deal. The team wasn't aware of the middleware or its fees before getting the bill, and it had to pay for a separate license for each platform. "It was a big hit financially, which put us at a loss in terms of the Mac and Linux ports," Briscoe says.