Skyrim Together Reborn (opens in new tab) is a mod designed for groups of two-to-eight players, though the creators have tested it with over 30, essentially making a mini-MMO. The aim is for friends to be able to play Skyrim co-operatively, complete with shared quest progress. Since its release on NexusMods yesterday, Skyrim Together Reborn has already been downloaded over 56,800 times. For comparison's sake, the second-most popular new mod added to Nexus is a sexy nun outfit (opens in new tab) from June, which has 30,000 downloads.
As well as the installation video above, mod developers The Together Team have put together both a guide to getting started (opens in new tab) and a playguide (opens in new tab), both of which they describe as essential reading. You'll need to be playing Skyrim Special Edition version 1.6 on Steam, ideally without any other mods installed barring the address library for SKSE plugins (opens in new tab), and should get a new character to the end of the Helgen tutorial quest before trying to connect to a server.
Skyrim Together Reborn doesn't support Skyrim VR, or any version of Skyrim prior to the Special Edition's 1.6 update. You don't need to own the Anniversary Edition add-on, however, and if you do The Together Team recommend disabling its additions.
It seems to be working for most players, with a few expected bugs and omissions. Weather and patrols aren't synced, which means the vampires added by Dawnguard won't appear for everyone, some players are seeing items and characters sliding along the ground (opens in new tab), and enemies are intermittently causing more damage than normal. There has also been some random nudity (opens in new tab), with one player reporting, "Played it last night with a buddy, played wonderfully except near the end of hour 2 we both became naked to each other". Apparently removing and then re-equipping armor should fix that one.
Adventurous players have begun testing mod compatibility, and finding some favorites work with minor issues. As one player wrote, "We even had some visual mods and skse64 with skyUi running and the only two real issues were the inconsistent damage and that enemies sometimes stayed alive for one of the other [after] a finishing move. But that was solved by a no killcam mod and we are having a blast with questing."
Skyrim Together Reborn is open-source, and while The Together Team plan to maintain it, their hope is that "new developers come in to help this mod reach new heights. There is still lots of work that can be done, like building a scripting API, implementing features like weather sync, doing additional bug and crash fixes, making quests smoother, or finishing Fallout Together."