With the release of Don't Starve's DLC pack Reign of Giants, Klei Entertainment has announced that a multiplayer expansion is currently in the works. The details are still fuzzy, apparently it hasn't evolved much past "hey, we should do multiplayer!" but the plan is to have the alpha out by the end of this summer. Most of the work is apparently going into balancing the game for two to four players, and you'll be able to play public games with strangers and private games with your friends. And, for those of you who prefer to die cold, alone, and clutching your axe handle like a string of rosary beads- don't worry, the adjustments are solely for the multiplayer games- single player won't be affected.
Klei promises that this will be a free expansion for everyone who already has the Steam and Standalone versions, but it will raise the price of the base game to $19.99. Which, coincidentally, is about how much it would cost you to get Don't Starve and the Reign of Giants DLC right now. Just sayin.