Blackboard recently announced the retirement of Bb Mobile Learn and the release of two persona based apps, Bb Student and Bb Instructor. These apps were to replace Bb Mobile Learn and it had been implied that Bb Grader (a standalone app for instructors to grade assignments) would be replaced by a full featured Instructor app.
I recently attended a webinar detailing the new Bb Instructor app and the grading functionality is scaled back from what is possible through a web browser. You may still need the Bb Grader App in the immediate future while Blackboard phases in grading functionality in the Bb Instructor App.