[PaulDavisThe1st]

help on VMS wasn't a builtin. It was a system-provided program, with data files that could be accessed via other software.

[JdeBP]

The same was true on MS-DOS, DR-DOS, and OS/2. Microsoft provided a help file compiler with some of its DOS development tools, and IBM provided an INF/HLP compiler and (if memory serves correctly) a message file compiler with the OS/2 SDK (HELP using both hypertext help files and message files on OS/2).