Creating Custom Assignments

Is there a way to make custom assignments that follow the course but are extra work? For example, for a history class, I want the students to make a timeline. This isn't an existing assignment in the course and I know I can assign this separately, but I'd like for them to have one place to see all assignments, including ones not included in the course. I'd also like to be able to load the grades for these assignments as well. Does this already exist and I just cannot see it?