Both the Omega Man and I Am Legend are based on the book “I Am Legend”, but each are presented in a different way.
Everyone on Earth ends up with a fatal form of agoraphobia so no one can go outside. The story follows a man who’s trapped in his office at work as he tries to escape and find his girlfriend.
Based off the Stephen King book of the same name, The Mist is the story of an end-of-the-world Earth that’s been shrouded in mist. While mist on its own is scary enough, this mist has monsters in it.
Children of Men is one of my absolute favorite movies of all time, so I’m glad to see other folks recommending it too. While it’s not fully “end of the world”, it’s post-apocalyptic in the sense that humanity is slowly dying out.