MuseScore is a free software to compose your music notes. It is a WYSIWYG Music notation program, and is licensed under GPL. Professional users will find MuseScore extremely easy to use, and feature rich.
Here are some of the features of MuseScore:
- Works on Windows, Mac, Linux.
- Notes are entered on a virtual note sheet.
- Notes can be entered by keyboard, mouse, or MIDI.
- You can directly create a sound file of your scores with File -> Save As… (WAV, OGG, and FLAC)
- You can import and export MusicXML and standard MIDI Files.