Not exactly the same but check out Kenshi. It's also more like Wasteland than it is like FO but i can't recommend it enough.
Post apocalyptic weird low-tech scifi sandbox.
Important to note, its completely open ended. No story. But quite a lot of stuff to do, factions to keep tabs on, settlements to build and manage, people to recruit.. lots of moddability.
You'll have to find your own purpose out there.
Oh and it's crippling difficulty can be daunting.