mus is: Mus stands for Finale Music note file format. These extensions can be opened by MakeMusic or Finale softwares.
These music files are created by note editing softwares called Finale or Makemusic. It may include audio content such as MID file, if it is created by MakeMusic software.
You can open these files with Finreader software. There are different websites to get it free. You can easily download.
Mus File format viewers or openers
Mus File related links.