For me man(3) is the most interesting of them all.
Run `apropos . | grep "(3)"`; you'll be surprised how many libraries come with man pages for their functions (e.g; curl).
Now I wonder if there are any IDEs that can automatically dial into these man pages and pull up documentation for functions?
There's guaranteed to be some sort of context-sensitive man plugin for vim &| nvim for shell scripts.
Also, have you ever seen the DOS Borland IDE context sensitive help UX?