UbiSoft has just announced Myst Online, a multiplayer version of the best-selling series. Here's some information from the press-release:
Devotees of the Myst series, fans of traditional massively-multiplayer online games, and non-gamers alike are sure to be captivated by Myst Online. The game features visually stunning real-time 3D graphics, rich storylines, continually updated content and real voice communication, and traditional text chat. Myst Online will have an easy learning curve, enabling players of all skill levels and interests to experience the expansive Ages and history of Myst in a uniquely social environment.
It's safe to assume that this is the title we have known for some time as Mudpie