FOMUS can output LilyPond http://lilypond.org/ files for processing into PostScript or PDF format. If you specify that FOMUS output an .ly file and the lilypond command is in your path then FOMUS automatically invokes lilypond for you, generating a .pdf output file. It should also automatically open a viewer application afterwards to show you the results. Unless you are running Linux, this should probably work out of the box (Acrobat Reader must be installed in the default location in Windows). If one or both of these two things doesn't happen, the following two lines should fix this if they are placed in the .fomus initialization file in your home directory:
lily-exe-path = "path/to/lilypond_app"
lily-view-exe-path = "path/to/my_pdf_viewer_app"
To send output to either of these two commercial applications, specify an output file with an .xml extension. This generates a MusicXML file which can be loaded using the Dolet plugin or a special import XML menu selection. See the MusicXML web site at http://www.recordare.com/ for a list of other software packages that import MusicXML.
FOMUS also outputs standard MIDI (type 1) files. It attempts to produce a file that accurately reflects the score on listening but is not necessarily useful as a means of importing into other programs. Each voice and percussion part in the score is sent to a separate MIDI channel. FOMUS adds additional MIDI ports to work around the 16 channel limitation, so if you have many parts it is necessary to use a MIDI player that understands multiple ports.