Fortress is the code name for a new game that has yet to be officially unannounced by Square-Enix. The game was originally being developed by GRIN, but because of issues Square-Enix placed the project in the hands of a new developer. Not much later GRIN officially closed down because of bankruptcy
This project has yet to be officially announced, but its existence was leaked out by GRIN's Development team during the takeover. It was first believed that the game was completely cancelled, but right now the game is still in development by an currently unknown studio, under the suppervision of Square-Enix.
The game will become an action game which takes place in Ivalice right after the events of FFXII: Revenant Wings, and it intended to become a multi platform game for the PS3, Xbox 360 and PC.