It is looking like a very fine year indeed to be a Fallout fan. Even if you're not on board with Fallout 76 taking the series online, we've got two full-game-length mods on the way, both due out before the end of 2018. Fallout: The Frontier is an unofficial expansion for Fallout: New Vegas, and has you heading to the frozen north to aid a crew of New California Republic deserters in a massive new map (as big as the editor allows) against a well equipped enemy force. Check out the dramatic and explosion-filled new trailer within.
Unlike the upcoming Fallout: New California (which is an entirely self-contained adventure), The Frontier is designed to integrate itself smoothly into your adventures through the Mojave and have you first getting word of the northern campaign after you've got a few quests under your belt. It's even designed to play nice with other major mods for New Vegas, including an overt recommendation that you use the Project Nevada gameplay overhaul, which I personally swear by.
On top of familiar sights such as ruined vaults, spooky caves, and miles upon miles of new snowy wastelands to explore, the trailer features some really interesting stuff, including tanks by the dozens, massive vertibird-assisted offensives, and even a full-fledged trip into space. Presumably you'll be trying to take control of the orbital death-beam that is shown wreaking havoc across the battlefield. There's even some more esoteric environments, including what looks like an abstract nightmare filled with wildly pulsating walls and flailing horrors. Spooky.
As with New California, The Frontier has been in development for years now and is apparently in the final stages of development. While the developers aren't quite ready to give a release date, it is in the latter phases of testing and should be out this year. Fallout: The Frontier will require the Ultimate Edition of New Vegas. You can find more info and more trailers on its official site, along with a list of supported/required/recommended other mods here.
For reference, New California is due out on October 23rd and Fallout 76 lands November 14th. Here's hoping for a mid-December release then, just to space things out a bit.