According to a post on the Myst Online Forums, the game is in development and will be released "...by early summer at the latest." Just in time for gaming at the beach!
Riven is the sequel to Myst, the adventure game that revolutionized the industry when it was first released for the Mac in 1993. The goal of Myst is to solve a series of complicated puzzles and ultimately answer the question, "What's going on here?" Riven is the sequel to Myst and describing its plot would reveal spoilers for both, so we'll let you play it for yourself.
Myst for iPhone was released last July to the praise of the game's dedicated fans. I've played both the Mac and iPhone versions, and am happy to say that the iPhone port is faithful to the original while the touch interface adds a whole new level of fun (don't click on that lever, go ahead and touch it!). With that in mind, I expect an equally pleasant experience with Riven for iPhone.
Of course, they'd both be gorgeous on the iPad (and huge -- the iPhone build of Myst is 533MB!), but we're getting ahead of ourselves.
[Via Touch Arcade]