Setting-wise? Nothing is really like Fallout. You need more than just "oh, nukes" to 'feel' like Fallout. It has a certain atmosphere, a certain focus on the setting over the protagonist and it has that certain spin that allows it to do more than other settings because of its lore (airborne FEV, 50's divergence).
Let's take Wasteland as an example and why it isn't like Fallout. There are mutants in the game. But they're not detailed. There isn't really an explanation for how they came to be, when that happened, where it happened. In Fallout we have a clear explanation for super mutants and ghouls, while still a bit vague, have strong evidence to back up certain theories. And because of the airborne FEV and the doctor up in Shady Sands talking about how radscorpions should not be able to mutate this way because of radiation alone, it gives the lore a whole different layer to its mutants and how they came to be. Things don't just mutate cause of teh lulz, no, they forcibly mutate and adapt to the environment around them because of the airborne FEV. But in Wasteland? What exactly is the different between a regular dog and a Nuka Pooch? How exactly did certain mutants come to be?
There is no game out there with the same 'feel' as Fallout if we're talking about post-apocalypse settings. Fallout used to be very strict about its lore, to the point that Chris A wrote a bible to correct anything they mucked up in Fallout 2. The setting of Fallout demands that lore be upheld, that things be explained, that everything makes sense within its setting. And far too many settings out there skimp out on the details or go back on their lore or leave it too vague so that they can use it as a loophole for whatever bullshit they can come up with in the future.
So you need a strict adherence to the lore, a narrative that is more focused on the world rather than the player, post-apocalypse with a spin (50's divergence) just to mention a few; I personally can't think of anything that is like Fallout when it comes to the setting.
And gameplay wise? Only game I've played that has a lot in common with Fallout is Underrail, but even it doesn't 'feel' like Fallout as it lacks certain things that I consider vital for Fallout gameplay.
I would only say that game X is like game Y if they are so alike that one might as well just be a TC mod because of how similar they are in gameplay. Otherwise? It ain't the same. If there are too many differences then they stop feeling the same and become their own distinguished titles. I'm very very picky about this and quite frankly there is absolutely nothing out there that is comparable to Fallout. Closest thing I've seen is Underrail and even that one isn't similar enough for me to consider it "like Fallout".
So if I have to stretch what I consider "like Fallout"?
Underrail.
The end.
Nothing else is "like Fallout" IMO.
