Multiple users on one pc

In my high school, one of the computer labs we had these devices that allowed three users to simultaneously log into three separate accounts on one computer and were able to do different things on each account without interfering with the other users. Each person had their own keyboard, mouse, and monitor, with all of it plugged into just a regular tower. My questions are: what is this equipment called, where can I find it, and how much does it cost?