There was one called xlsfonts which would list all the available fonts.
https://www.x.org/archive/X11R7.5/doc/man/man1/xlsfonts.1.ht...
https://www.x.org/archive/X11R7.5/doc/man/man1/xlsfonts.1.ht...
It is a command line tool and can be used without a GUI. You can even query for the fonts on another X server's display (1). See this excerpt:
-display host:dpy This option specifies the X server to contact.
(1) - where the meaning of server and client is the reverse of that of traditional client server.
Its fun to query or set information on a remote. The same applies to xdpyinfo, xset, xrandr and many more support the -display option (if they don't then set the DISPLAY environment variable).