Doom was famous for being one of the first Multiplayer PC games. There is an old anecdote about how John Carmack noted that it would be pretty easy to add network multiplayer to the code he was writing and John Romeo's eyes practically flashed dollar signs.

Of course as an afterthought it had a couple of issues. The primary one being that the framerate was locked to whomever had the slowest computer. Probably drove PC sales as you did NOT want to be the guy who showed up to the LAN party and tanked everyone's FPS.