MuseScore is a free, open-source music notation software that allows users to create, playback, and print sheet music. It's cross-platform and multi-lingual, and comes with an easy-to-use WYSIWYG editor that supports audio score playback to create visually and audibly appealing music scores.

Some of the features supported by MuseScore include the ability to create unlimited score length and an unlimited number of staves per system. With up to four independent voices per staff, users can explore a wide range of musical compositions. The program also features a score creation wizard and templates, making it easy for users to get started.
MuseScore supports automatic part extraction and transposition, as well as repeats, including segnos, codas, and measure repeats. The program also supports dynamics, articulations, and other expression markings with playback support for most, as well as custom text markings, lyrics, and chord symbols. For jazz notation, MuseScore includes lead sheets, slash notation, and a handwritten font for text. The program also supports swing and shuffle playback and offers a mixer for instrument levels and effects.
For percussion notation, early music notation, and cross-staff beaming, MuseScore has users covered. The program also supports importing of graphics, custom key signatures, and additive time signatures. MuseScore offers user-defined score styles, giving users the freedom to customize their music notation.
Most elements in MuseScore are laid out automatically, but the program also allows for manual positioning. The program's capabilities can be extended via plugins, and the growing repository on musescore.org contains many plugins submitted by users. MuseScore comes equipped with a set of sounds that reproduce common instruments, without taking up tons of disk space or memory. Users can also substitute any SoundFont they prefer for more variety.
MuseScore can import and export MIDI and MusicXML files, as well as import from Capella and other programs. The program can export to PDF, PNG, and other graphic formats, to WAV and other audio formats, or to Lilypond for an alternative layout and print option. Users can also upload scores directly to the score sharing site musescore.com. Program support is provided on musescore.org, making MuseScore a great choice for music notation software.
Version 1.1: MuseScore 1.1 comes with a new jazz font and makes the creation of lead sheets much easier. It also embeds a Twitter stream for the latest news and YouTube tutorial videos to learn about the software. It features sheet music shared by the MuseScore community which can be downloaded for free.
Version 0.9.6.3: Ready for basic ensemble scoring; Support for nested tuplets; Playback for all general midi instruments; Auto save; Plus hundreds more improvements
Version 0.9.6: Ready for basic ensemble scoring; Support for nested tuplets; Playback for all general midi instruments; Auto save; Plus hundreds more improvements
Version 0.9.4: http://www.musescore.org/en/blog/2009/02/06/new-features-musescore-094