A leaked screenshot from another "Assassin's Creed" looks to be "Assassin's Creed: Rising Phoenix", according to All Games Beta.
Two figures can be seen in what look like hazmat suits with the Abstergo logo emblazoned across the back. The eerie light is not dissimilar from the one seen in Grand Temple where Desmond and company spent much of their time in "Assassin's Creed 3." If this is the case, it would seem to indicate that "Rising Phoenix" would take place almost directly after the events of "Assassin's Creed 3," and the title could allude to a possible return of Desmond.
The first shot that leaked seemed to indicate that the hacker group Erudito would make another appearance as well, their own logo seen on a banner in a warehouse.
Not much more information has been ascertained, but online Spanish store XtraLife had the game listed as a PS Vita release for October 10. The listing has since been pulled, but not before AGB grabbed a screen cap of it.
Ubisoft has yet to make any official statements regarding the game.