Harker was a video game being developed for the PlayStation 3 & Xbox 360 by Double Helix Games. The game was said to be based on the fictional character Jonathan Harker, a vampire slayer.
In the trailer, Harker was perceived as a much more efficient and couragious vampire hunter, as opposed to the classic portrayal of Jonathan Harker in the Bram Stoker’s books and films, including Dracula. It was said that you take on the role of Jonathan Harker in the 18th century and try to rid the world of the unholy vampires.
Double Helix studios put the game on indefinite hold for the development of Silent Hill: Homecoming. Whether or not they plan to continue production of the game is unclear at this point. [Infos from Wikipedia]