Rather cryptically described as "An exploration-puzzle game on an uninhabited island", the new game in development by the creator of Braid now has its own blog here.

In the meantime here's some concept artwork to ponder... interesting stuff and the blog describes The Witness as being a "very visual" game... intriguing, huh?  I'm hoping it's not going to be like Myst though... never could get into that game series.