Square Enix's role-playing game Final Fantasy XIII is a PlayStation 3 game (and an Xbox 360 game!). But at one time, the game was running on the PS2.
Early artwork and screens have been published in two new books from Square Enix, giving insight into the game's design process. These test version images pre-date E3 2006, when the game was announced, and thus, are logically running on the PS2.
The art direction is different than that which appeared in the final product, and the character models look to be stand-ins for the test version. The battle user-interface, however, doesn't look that different.