MuseScore is a free cross-platform WYSIWYG music notation program that offers a cost-effective alternative to commercial programs such as Sibelius and Finale. You can print beautifully engraved sheet music or save it as PDF or MIDI file.

Features:

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 your keyboard, mouse, or MIDI keyboard

Integrated sequencer and FluidSynth software synthesizer

Import and export of MusicXML and Standard MIDI Files

Available for Windows, Mac and Linux

Translated in 43 languages

GNU GPL licensed