iPhone and iPod Touch, notes WhatTheyPlay. The $6 app is a hefty 700MB, so the developers at Cyan Worlds probably aren't kidding when they state the "original Myst sights and sounds have been meticulously re-assembled ... in a format where a simple touch or swipe moves you through the world."
The game features the full Myst experience -- allegedly "better than original Myst" -- with auto-save, bookmarking and (most importantly) quick access to the hint guide. We haven't had a chance to check it out, so let us know how Cyan Worlds did porting the game for portable play.
iTunes - Download Myst at the iTunes App Store