After much thought, considering all the various computers I have owned and used, I suddenly realized that my favorite computer of all time is the CERL PLATO system at the University of Illinois, circa 1980.
It was a dual mainframe timesharing system, designed for computer-aided instruction. The terminals were 512x512 pixel plasma graphics displays, and the keyboards had unusual keys like BACK, LAB, DATA, MICRO, and an assigment arrow that looks a little like this:
<=.
It had personal notes which worked a lot like email, general notes which worked a lot like newsgroups or web forums, and "TERM-TALK" which worked a lot like instant messaging. It had multiplayer games like Empire (based on Star Trek) and Avatar (modeled after Dungeons and Dragons). There were individual terminals in many locations, small clusters of terminals in many more, and a few "classrooms" with dozens of terminals in one place. Most of the terminals were in the Champaign-Urbana area, but there were others at Kennedy-King College, and at the UI Chicago Circle Campus, and at Indiana University in Bloomington. My fiancée and I were at separate colleges and used to chat with each other over the system.
I miss PLATO.
PLATO People were a great bunch to hang around with.