Comment by _b8r0

There isn't really a single program. Man pages have been built through convention by people who've taken the time to write them, at various points following guidelines from Ritchie et al. It's usually down to the OS to explain the purpose and function of man pages in their own documentation.

For some Operating Systems, man pages are exceptionally high quality (most notably the BSDs). For some, they're bilge, but such systems tend to have init managed through systemd.

Having said that, many OSes support info(1), which provides more detailed software manuals for many pieces of software.

Of course, there are actual physical locations for forms of documentation not in man format or structure. You can find out where such documentation lives on your system on most Unix-like OSes through man:

$ man hier