This comes up periodically. Here is the status in my mind--Scoring programs:
Mscore (musescore) -- promises to be the linux opensource Noteworthy or
Sibelius. No upgrades recently; had stability problems. Author made UI
decisions I would not have made which does not make them bad or wrong. Does
its own engraving, quite nicely if one could only get the whole song done.
QT4--had some speed problems scrolling large scores.
Nted -- one of the successors to Noteedit. This is being continuously upgraded
and work nicely, is WYSIWYG, does it own engraving, but can also run Lilypond.
Fairly complete. Still a few annoyances that stop me cold in some scores.
Canorus -- the other successor to Noteedit. Have not heard anything on this
one lately. Last version was not ready to play.
Denemo -- GUI WYSIWYG front end for lilypond. Latest and greatest claims to be
ready to play but I cannot compile it on my Debian box. Versions in the repos
are very old and very useless.
Rosegarden -- most developed of the Linux MIDI/audio all-in-ones. Is a KDE3
app which will not run on KDE4. Found its scoring part very difficult to use.
Note that most all of these start off with restfull measures. Fine for
entering notes but problematic for editing or moving note-sequences around.
Most of these do MusicXML which means one can transfer data among them.
All said and done, the one in which I know I can start a song and actually
finish it is ... Noteedit, the old KDE3 program which will run fine on KDE4
(ignore any error messages). Notedit cannot copy and paste but one can enter
notes any way one wants and worry about rebarring/rebeaming later on. It
outputs to Lilypond (there are sometimes errors) and MusicXML (as well as MIDI
and ABC). Its XML is missing chord-names and when imported into mscore, that
feature will be unsavable there as well.
Lilypond frontends (if you want to get into its command language--sort of a
cryptic blend of TeX and LISP):
(Denemo is a GUI/previewing score program, above, not a command editor.)
Lied -- a Lilypond markup editor with loads of huge dropdown menus for
entering commands. Compiled with Fastlight. FL supports UTF8 but lied will not
display non-Latin characters correctly.
Frescobaldi -- funny name for a nice python frontend with a preview pane.
Latest and greatest segfaults on my box but this is a promising program for
diehards that want to edit Lilypond files directly!
Kate-plugin -- for KDE Kate users, there is a plugin for editing Lilypond
files. I have not tried it.