LF Game Engine Style Multiplayer Building Game

InfusedEMP

I've been searching for over 10 years for something like this and have been unable to find it.  What I want is a multiplayer game engine that will allow me to build game worlds in real-time with other people - places that look like Lions Arch and Queensdale from Guild Wars 2 or Stormwind and Elwyn Forest from World of Warcraft.

In 1998 I started playing a multiplayer chat interface 3D building game called Active Worlds.  In Active Worlds I was able to build anything my imagination could come up with, and other people could help me build it in real-time.

In Active Worlds I was able to use a 3D modeler and scripting to create any object I could imagine - be it a bridge or a mine shaft or a chair - texture map the objects, and upload them directly into my worlds server for instant use within the world.  I could also edit the terrain, add fog, ambient lighting, a skybox with clouds, create avatars, add script to make things happen, etc.

I played Active Worlds for years but they eventually started charging astronomical fees and it became antiquated.  The graphics look like late 90's graphics and there is no way to add game elements such as mobs or quests.

After Active Worlds came Second Life, which was a direct rip-off of Active Worlds except they charged for absolutely everything and had far less game-world style building features.

After Second Life came Minecraft, which was about 100 steps and years graphically backward from Active Worlds and only allowed building with blocks.

In all my research I keep coming back to game engines.  They seem to be the only thing that will allow me to do what I want to do.  I want to design full, beautiful game worlds with modern (preferably post-2010) graphics using scripting and 3D modeling programs.  The thing game engines are missing though is a multiplayer interface.  I'm not much of a singleplayer type of person.  I want to be able to do what a game engine allows me to do except in real-time over the internet with a group of friends with avatars representing our current view-position within the under-construction game world.

Does anyone know of anything out there that will allow me to do this?  Thanks!