SlackBuildsOrg/multimedia/MuseScore

MuseScore is a free cross platform WYSIWYG music notation
program, licenced under GNU GPL.
MuseScore has been rebranded to "MuseScore Studio" to avoid
confusion with the site musescore.com that holds the music scores.

MuseScore features:

 - WYSIWYG design, notes are entered on a "virtual notepaper"
 - TrueType font(s) for printing & display allows for high quality
   scaling to all sizes
 - Easy & fast note entry
 - Many editing functions
 - MusicXML import/export
 - MIDI (SMF) import/export
 - MuseData import
 - MIDI input for note entry
 - Integrated sequencer and software synthesizer to play the score
 - Print or create pdf files

In Slackware this package partially installs to /opt/MuseScore