MuseScore Portable, via PortableApps, is a free and Open Source music notation program that offers a cost-effective alternative to commercial programs such as Sibelius and Finale. Installer, Linux, Mac, and Android are also available.

MuseScore Portable facilitates printing beautifully engraved sheet music or saving it as a PDF or MIDI file. MuseScore Portable supports unlimited staves, including up to four voices each. It also supports dynamics, articulations, lyrics, chords, lead sheet notation, import/export of MIDI and MusicXML, export to PDF and WAV, plus you can share your score online.

MuseScore will help you write music for Piano, Guitar, Orchestra, Jazz, Choir, Band, Marching, and much more.

To create a new score, use one of the following options:

In the Home: Scores tab, select New score, or click New (bottom right).
From the menu, select File→New.
Use the keyboard shortcut, Ctrl+N (Mac: Cmd+N).

Adding instruments is equally simple; click on the instrument name to select it, and click the → button to add the instrument to your score (Pro tip: double-clicking an instrument name does the same thing). Instruments are automatically arranged according to the order in the dropdown menu under Your Score.

Full handbook available here.

MuseScore 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

Installer, Linux, Mac, and Android are also available.

  Download