LilyPond!

MuseScore is a free music notation and composition software available for Linux, Windows and Mac.

With TuxGuitar, you will be able to compose music using the following features

OpenMPT (short hand for Open ModPlug Tracker) is a popular tracker software for Windows. OpenMPT is completely free and allows you to create and play back some great music on your computer. Based on the original ModPlug Tracker written by Olivier Lapicque, OpenMPT is free software and supports a wide variety of module formats and offers an intuitive, native GUI as well as advanced features such as VST plugins and ASIO output.

Rosegarden is a well-rounded audio and MIDI sequencer, score editor, and general-purpose music composition and editing environment.

Sibelius is the world’s best-selling music notation software, trusted by top composers, publishers, and students alike. With Sibelius 7.5, you can express, accelerate, and promote your creativity in more ways than ever before, enabling you to deliver beautiful, professional scores faster and share audio and video versions of your work—with stunningly realistic musical phrasing—to make your talent stand out from the crowd. It’s the fastest, smartest, easiest way to write music for live performance, film and television, media entertainment, or in the classroom. »

Anvil Studio is a free Windows 7/Vista/XP/2000/98 program designed for people who want to: -- record music with MIDI and Audio equipment, -- compose music for MIDI and Audio equipment, -- sequence music with MIDI equipment, or -- play with music using a computer and sound card.

Finale is proprietary scorewriting software developed by MakeMusic, Inc. It displays music primarily in music notation and allows for multiple tracks and very specific tweaking of instrument sounds for each track.

Music21 is a Python-based toolkit for computer-aided musicology.Applications of this toolkit include computational musicology, music informations, musical example extraction and generation, music notation editing and scripting, and a wide variety of approaches to composition, both algorithmic and directly specified.

Impro-Visor (short for “Improvisation Advisor”) is a music notation program designed to help jazz musicians compose and hear solos similar to ones that might be improvised. The objective is to improve understanding of solo construction and tune chord changes. There are other, secondary, things it can do, such as improvise on its own. It has also been used for transcription. Because rhythm-section (e.g. piano, bass, drums) accompaniment is automatically generated from chords, Impro-Visor can be used as a play-along device. Now having a wider array of accompaniment styles, its use is not limited to jazz. »

ABCJ is a pure-Java editor, player and librarian for music files stored using Chris Walshaw's ABC notation.

StaffPad is a brand new class of notation app, designed to take advantage of the advanced pen and touch input found on Microsoft Surface* and other compatible Windows 8.1 devices. As you write notation using the pen, StaffPad recognises your handwritten music and converts it into a beautifully typeset score which you can further edit, playback, print and share. StaffPad combines the best of working on paper with the best of working digitally, evolving the same process that's been used for hundreds of years to write countless masterpieces. Natural pen input, detailed orchestral playback and powerful score editing features mean that StaffPad is perfect for professionals, and easy for beginners. For the first time, an entire orchestra is available at the tip of your pen. Getting StaffPad is easy - it's available exclusively on the Windows Store. What will your masterpiece be? »

Next-generation 64-bit scoring software for OS X and Windows, designed by musicians for musicians Beautiful engraved output with unrivaled attention to detail Flexible note input and powerful editing, including ability to insert and change duration of existing notes Streamlined, single window interface puts every tool at your fingertips

EasyABC allows you to edit and play abc files. It supports conversion from MusicXML and MIDI to ABC. The latter uses a custom implementation (midi2abc is not used) in order to produce very readable ABC output. Direct midi input is supported for people with a midi keyboard. It uses abcm2ps for printing music and abc2midi for playing it.

NtEd is a GTK+ score editor. It intends to be really WYSIWYG: what you see on the screen is exactly what you get on printer output. It supports up to 4 voices per staff, drum notes, 5 lyrics lines, N-Tuplets, context changes, repeats with alternatives, configurable music instruments per staff, MIDI / MusicXML import, PS / PDF / SVG / PNG / Lilypond / MIDI export. Scores can be played through the ALSA sequencer.