More than one map running at the time in a network game

I will like to drop a request about a system to handle more than one level at the time with a max of levels in run, what i like to say is something like the Starbound, Diablo, Torchlight systems, a coop games or multiplayer games (no mmo) where with the support of a singles server process or a p2p system with one host only you can handle multiple maps at the same time running.

For example when you run a server for Starbound in your computer, you can be in the map 002 and your friends in the map 005 with AI in the both maps, and when the players exit from one map then the server close/unload the map and probably you can set here the max of levels loading at the same time and if someone try to load another map then you get a lock until one of the loaded maps are unloaded.

Then that is the request add a system to handle more than one map loaded with all components and network support. (A simple system for coop or normal multiplayer games).