Just made a news post about this, but figured I should post it here if people actually wanted to see it.
Fortress was/is an unreleased, unannounced (and apparently not-yet-canceled) FF12 spinoff that was being developed by Grin. They only worked on it for a few months before Square-Enix 'took' the game from them, but some footage from those few months of development has surfaced.
You can see it at Gamevideos: Leaked Footage of FFXII: Fortress from GRIN Video from GameVideos
...or at the Designer's site (2nd video): Jonatan Crafoord - Audio Designer
In case any of those videos get taken down, I have saved it to my computer. Word has it that Squenix is still going to work on the game in some form.
You can look at some of the concept art here.