With ftp and SSH virtual filesystems available for such site an OFM is a quintessential Webmaster tool. This unique role that OFMs can play as a webmaster IDE fuels my interest in the field after more then two decades of usage.
Along with integration of file managers, internal viewer and editor OFM also integrate functionality of a dozen command line utilities including, but not limited to: There is a large variety among OFM implementations.
That means the quality of shell terminal window provided is of paramount importance for OFMs and the role of user menu is central.
They can also serve the role of IDE for webmasters of the sites that use plain-vanilla HTML (as opposed to database driven sites).
Several programs belonging to this type are descendants of Norton Commander, a file manager first released in 1986 by Norton Computing (since 1990 Norton Computing became part of Symantec).
But not only file managers can have this type of interface.
See my article Less is More: A rich functionality behind Spartan interface of Orthodox File Managers for more information on the topic.
richer functionality then alternatives (and while it's just accidental that one of popular OFMs is called FAR, we can claim that it was God's hand which guided the author to chose this particular name :-).