A sequel to the 2003 game XIII looks to be in the works after Anuman Interactive released an image on their Facebook page teasing a sequel to the 2003 Cel-Shaded FPS based on the comic series of the same name. XIII ended with a message saying TO BE CONTINUED but since then nothing has been heard regarding a sequel, and many had assumed that the story of the original would remain unresolved.
The original XIII was based on a series of comics of the same name and was developed and published by Ubisoft. It recieved pretty good reviews with reviewers praising the unique art style and presentation elements as well as the game's fun multiplayer.
The teaser might not necessarily mean that this is a sequel to the first game, it could well be a prequel or even a HD re-release. The teaser mentions that the new XIII game will be coming to PC, Mac and iOS. A detail which lends itself to the re-release idea. It could also be a spin-off of some kind, since there is plenty of story in the XIII comics that wasn't covered in the game.
Anuman Interactive have yet to confirm anything but fans of the original should remain on the lookout for news.