MuseScore, a cross-platform WYSIWYG music notation program, is free and open-source. It's licensed under GNU GPL.
- WYSIWYG, the notes are entered on a virtual note sheet
- Unlimited number of staves
- Staff can have up to four voices
- Quick and easy note entry using keyboard, mouse or MIDI
- Audio playback of the score
- Import and Export of MusicXML and standard MIDI Files
- Available in more that 50 languages