The Elder Scrolls III: Morrowind was released in 2002, but it's on the verge of experiencing new life through multiple revival projects. One of those is OpenMW, which aims to port the game to a new open source engine optimised for modern computers, with robust editing tools, and as of the first early test shown in a video below, multiplayer.
It's obviously pretty early: the two instances of the game seem to be running on the same computer and only simulating, I assume, the sending of data packets that would normally be tossed over the internet or network cable. As a first test however - to check the synchronization of position, inventory, race info, player attributes, and animations between different instances - it seems to work. OpenMW is open source, so anyone can fiddle with its codebase and have a go at implementing things like this, so it remains to be seen where it will go and whether we'll one day be riding Silt Striders with friends.
OpenMW has been in development for years and the current build lets you explore Morrowind environments with little or no mechanical interaction with the world. It does have a fancy new renderer as of November last year however, and progress has been consistent enough that I believe it'll eventually receive everything listed on its roadmap.
It's also worth noting that OpenMW is simply an engine and it requires the original Morrowind files if you want to play it. Morrowind-to-Skyrim port Skywind is the same, which hopefully puts them both on the right side of copyright law.
You can download the current build of OpenMW - which does not include multiplayer, I stress - for Windows, Linux and Mac OS X.