Thought I'd respond to your post from "how long"-thread here, to not derail from the topic. UDK would be quite easy to implement in a site like this as another "branch" I would say. It is sort of a "kit" to develop games using the unreal engine. So it is kind of a world/map/game editor.
It is fully customizable to create whichever game you'd like to create. It would also make all of us the possibility to create models for the same engine, or icons and sounds in the same format. Also terrains, user interfaces and cinematics are things you can do in it. Similar to our current WE.
I have to admit though, I am not that well-read on the subject of UDK, so my knowledge is quite small about it. But if you care to check it out, feel free to do so. To me it seems like something you could be looking for, if we are to branch out. I think one can even create games/applications for android, ios and consoles.
It is also free of charge.
link