why would you make a singleplayer-only doom mod that only works on the source port designed for multiplayer
That mod is intended for CO-OP and CAN be played solo if you want. Devs are emphasizing co-op and that's why they made the mod for zandronum.
What 1motlok here said. It's best played Co-op. We recommend using TSPG to host a free server to play with your friends!
