Partial Finish to Start + Start to Start
Sometimes a task is not dependent on another task finishing, but rather is dependent on another task being near completion (ie. Task 8 is scheduled to start when Task 7 is 1 week away from completion).
Similarly, it would be beneficial to be able to schedule two tasks to be predicated on each other (ie. Task 8 is scheduled to start at the same time as Task 7 - Neither 7 nor 8 can begin without the other).