Multiplex Nether Portal
First, you need to build a vanilla nether portal. If you are done you have to place a sign below the portal with the word portal
in the first line. Make sure that the obsidian above the sign has air above it. Now the sign only needs a redstone signal to open a navigation GUI. In the GUI you can select your target destination and unlock other dimensions like the End, Twilight Forest etc.
How to build:
The video below will show you how to setup the portal for our 1.7 servers:
The video below will show you how to setup the portal for our 1.10 servers: