I apologize, I have no idea what these are meant to be called:
You go to the post office, or whatever, you take a number. Your entry time is registered in a computer somewhere, and optionally you're given an estimate of how long it'll take until it's your turn. Number shows up on a big dashboard/TV, and the person behind the counter can manage the queue - mostly pulling up the next number in line.
What are these systems called, and are there any recommended brands? Simplicity and ease of use are key.