Ask HN: What algorithms do you use to handle time based event?

Lets say you are writing a program that should send notifications at a user defined date. For example, a tasks management application should send notifications at the due date of the task, defined by the user. Any date can be inserted at any time in the list of "notifications" to send.

What algorithms would use? The best answer to that question was for me to use a priority queue.

I am curious to learn about alternative to that problem.