As a longtime fan of the Myst games I'm rather surprised that I have not heard of this before but, a team of Myst fans have been making a realRiven in real time 3D, they have even got the blessing of Cyan who have also offered some support although due to contractual obligations with Cyan they can't go into details. Obviously, this is a long term project but they release frequent updates and videos on youtube and their work looks very impressive although it should also be pointed out that this is very much a work in progress, many textures and objects are either temporary placeholders or missing, more info on their website @ Starry Expanse.com
