You should check out 'Threads' a UK TV movie from the mid 80's. The effects are wonky by todays standards but it's still chilling as hell. Fail Safe and Forbin: The Colossus Project are also still scary.
Children of Men is my favourite film of all time. A flawless masterpiece with great characters and so plausible.

+1 for Threads, superb. They could act, the director could direct; I'm critical of much of todays loud, effects heavy drama. But then I'm a wrinkly 8)

"Apocalypse Now" fits into the category I think, if you haven't seen it - do so asap.

I have seen apocalypse now, didn't think of that when I wrote the post. I guess it's not a proper apocalypse (global/taking humanity to near extinction - does tick the societal collapse box) but the name certainly fits and it is a brilliant film.

Apocalypse now is one of my favourite films. Have you seen the redux version. It’s a directors cut and is so worth it. It is loosely based on the book Heart of darkness by Joseph Conrad which is a good read if you enjoy the film. Brando is the man. A hell of a lot of his part is improvised. Genius

I actually prefer the original version, it's tighter (and usually I'd always go for director's cut). The Redux one felt a bit over-indulgent (the scenes with the playboy bunnies and the weird, detached posh French people were interesting but didn't add much that the film didn't already get across in other scenes, and they affected the pacing for me). Anyway, that's just my personal preference - great shout from you and Dirigible, and one of my favourite films too (also Conrad is one of my favourite writers). 

The "making of" doc for the film (called 'Hearts of Darkness') is an apocalypse film in itself ;). Def worth seeing if you haven't - at one point Coppola tells his wife that he's mortgaged everything he owns to pay for the movie, and it's going to be rubbish, and considers deliberately injuring himself to get the insurance payout ;(

Brando is indeed the man! I think he had to improvise most of it because he couldn't/wouldn't learn the actual script haha (plus the script was unfinished)...and yet the performance is still genius.

(also, Brando wasn't the only one who wouldn't learn his lines, as the link with Dennis Hopper above shows. And I'm pretty sure Coppola was partaking of the magic herb during shooting as well, let's not assume he was sober just cos he's the director ;)

This is all a tangent but man I love the film.

I was going to suggest The Road as well, as someone has already said - bleak and powerful film. And Children of Men is a great choice. Also, Tarkovsky’s Stalker - incredible shots and atmosphere.

I suggested it fits as the Vietnam War caused the collapse of Vietnamese society & economy, not to mention the USAs use of the defoliant Agent Orange, napalm and all the rest. As far as all those agrarian villagers were concerned it was an "extinction event", their world had gone. 8(

The Vietnam war was truly ghastly :(

Children of Men: that is my fav film ever, I remmeber when I first watched it I was so moved I was in tears. Usually love movies but never get emotional, Children of Men however got me. "Strawberry Cough". 28 Days Later, one of Danny Boyles movies.
Other good movies: Train to Busan, The Road, Cloverfield, 10 Cloverfield Lane, Shaun of The Dead, Sunshine (about a space crew in the future trying to stop an impending apocalypse as the sun is dying), Independence Day. That's what I can think of so far, but amazing shout on Children of Men, a lot of people I know have never seen Children of Men, it's a very underrated film.

I’m going to throw Snowpiercer into the mix. The movie, not the tv series. Directed by Bong Joon Ho, he directed Parasite and has a great name.

Children of men is also one of my all time favourites, very moving film that scarily looks like the not too distant future.

The walking dead( rv series )
The road
The book of eli
Night eats the world
Train to buscan
Last man in earth *TV comedy
A quiet place
The crazies
Just a few I have watched that were decent

Great list so far, just going to add:
Mad Max trilogy.
This is the end.

The Road is great.. really dark. Annihilation is good too.

World War Z was quite watchable if I remember, been a while since I’ve seen it though

A Boy and his Dog is a 70s classic!