http://blog.wired.com/games/2007/09/final-fantasy-x.html
It's currently only announced for PlayStation 3, but Square Enix's Hiromichi Tanaka said in his keynote address at Austin GDC that Final Fantasy XIII is being developed with a "cross-platform" engine:
"Development is proceeding smoothly now, with the framework now beginning to take shape. Last year we went through a development reorganization, with the development of our own cross-platform middleware – the white engine. This is the foundation for FFXIII and the new MMO."
The "new MMO" he refers to is an as-yet-untitled project that is indeed multiplatform. But the White Engine, up until this point, had always been referenced as PlayStation 3-specific. While this doesn't mean we should expect the game on more platforms, it certainly opens the door quite a bit more."