Dungeon Defenders – also, Trendy kinda said that on its website.
This time out the kids from the first game are all grown up and will participate in cooperative and competitive dungeon defending. The cooperative mode is a "true sequel" to the first game with more heroes, towers and obsessive loot stat comparisons. Trendy also mentions a "24-player overworld" is in the works.
The competitive mode is a Multiplayer Online Battle Arena (MOBA) set in the Dungeon Defenders universe. Trendy describes it as a "streamlined MOBA [that] aims for a shorter learning curve and more RPG-esque take on the genre."
No consoles have been mentioned for the sequel, which is a free-to-play game currently in development for PC, Mac, iOS, Android and "web." The cooperative mode will go into beta later this year or early 2014; the competitive mode is in closed beta with sign-ups available.