Stumbled upon a very interesting article today. Not exactly massive, but apparently the first (or 2nd?) multiplayer "video game" was designed for oscilloscopes in 1958. The first networked computer game with avatars and in game chat was another one that I've never heard of called Maze War. It dates back to 1973 (!).
The video of the oscilloscope game is labeled "the second ever computer game." This doesn't seem technically correct since it's not on a computer. And I really have to wonder what the "first ever computer game" was (and was it for oscilloscopes? televisions? slide rulers?). Of the games on that site, Space War was the only one I had heard of before yesterday.