You've actually heard of Rift: Planes of Telara before, it was just called of-telara-shows-some-early-promise-serverside-135004.phtml">Heroes of Telara at the time. The game, which is a fantasy MMO, is being developed by Trion Worlds. They're taking a different approach to the whole MMO thing by having all the game's content and updates handled on servers (cloud computing) while graphics and sound are handled by the player's equipment.
This means that the game world can be updated with minor or large details or events at any time without everyone having to get an update. That plays right into the rift part of the name of the game. Trion has explained that the world of Telara is being torn apart by rifts that cause changes to the world from entire areas being unlocked to unique instances of monsters attacking.
I'm not an MMO player, but having a world that can change easily on the fly sounds awesome. We'll just have to wait and see until 2011 when the game is scheduled to land on PC.