Denemo is a sheet music production software that adds new releases with new additions, bug-fixes and improvements. If you're looking for free software to make sheet music with high-quality notation, then you might try Denemo. I have been using this free software for some time now and I really like it. The biggest drawback is that if you don't have Windows it will not work on your computer. I use it on my Windows machine but other Mac users should look at other options such as FlexiMusic Composer or Fruity Loops Live.
Denemo is an open-source cross-platform software for MIDI editing and composing and recording. You can use it to record audio or to edit and re-record audio. It has many useful features including recording/editing midi files, exporting and importing of midi data, editing tools for tracking/capture and mixdown, support for VST and PC automation and virtual keyboard. It also includes some popular standard VST instruments and some interesting and unique instruments such as the "virtual piano", which is like a physical piano except that it responds to keyboard messages. You can save sheet music as PDF format and export files as midi format text files.
This editor was written and developed by two men, Laszlo Biro and Oliver Robbins. It was intended for music educators but due to lack of time, it has been used extensively as a general midi editing and composing tool. Currently there are many versions of the software available for both MAC and Windows. For a quick trial please download the demo version and check it out for yourself.