Vancouver developer Klei Entertainment Shipwrecked, the expansion pack coming to Don't Starve, will out on Steam Early Access December 1st.  The expansion, whose development is being assisted by Capy Games, will not require the previous expansion Reign of Giants, and taks players to survive in a tropical archipelago.

"The early access version of the game is fully playable, but there is still some work to be done. The initial version contains new seasons, creatures, biomes, and many other exciting ways to die. As always, during early access we will be releasing regular updates containing new content as well as tweaks and bug fixes based on your input. Remember, we’re listening, so join our forums and share your thoughts!"
 

You can check out all the details at Klei Entertainment's forum post.  Currently the expansion is only planned for PC