runoff-style typesetting systems predate Unix. In fact, to procure the PDP-11 to further develop Unix, the proposal was to create a system specifically designed for editing and formatting text.
``At the time of the placement of the order for hte PDP-11, it had seemed natural, or perhaps expedient, to promise a system dedicated to word processing. During the protracted arrival of the hardware, the increasing usefulness of PDP-7 Unix made it apprpriate to justify creating PDP-11 Unix as a development tool, to be used in writing the more special-purpose system.'' http://cm.bell-labs.com/cm/cs/who/dmr/hist.html
*roff probably would have died out, but James Clark wrote a free clone that is present in nearly every free unix distribution. Groff lacks many limitations that were in the original *roff and it has been used to format man pages, papers, and sizable books.
My personal attraction to groff has two parts. First, even though it isn't in widespread use, it's everywhere. Second, it formats great to both text and graphic devices. Groff outputs ASCII and postscript, and recent versions generate html (albeit poorly).
I've heard people complain that groff documentation isn't easy to find. For a period of time that was somewhat the case. This web page points to some free information about *roff.
You will need a postscript viewer to read most of this documentation.
My email address is bencollver at-sign gmail.com