I'd like to have a service that notifies me of deadlines. I input a description of the task and the date, all my tasks are then ordered by how close the deadline is. I can also set intervals for me to be reminded about the deadline.

I can share this information with someone like my boss. She can view what I'm working on and add tasks to it if need be, and every time she adds a task I get a notification asking me to accept the task. In addition to being able to accept the task, I have the ability to propose an alternative date too.

Simple.