MuseScore is a free cross platform WYSIWYG music notation program, licenced under GNU GPL. Some highlights:
* WYSIWYG, notes are entered on a "virtual note sheet"
* Unlimited number of staves
* Up to four voices per staff
* Easy and fast note entry with mouse, keyboard or MIDI
* Integrated sequencer and FluidSynth software synthesizer
* Import and export of MusicXML and Standard MIDI Files (SMF)
* Platform independent code, binaries available for Linux and Windows
* Available in 15 languages
* GNU GPL licencedMuseScore is available in English, German, French, Dutch, Spanish, Italian, Portuguese, Russian, Galician, Turkish, Brazilian Portuguese, Hindi, Danish, Finnish and Swedish.