Frescobaldi

Frescobaldi is a free GUI LilyPond sheet music editor. It strives to be lightweight and easy to use, yet powerful. Some of its features include:

• Syntax highlighting
• Auto-completion
• Point and click from the PDF display
• A MIDI player for audio "proof-listen"
• A Score Wizard to set up templates for editing
• A snippets library, extensible with own needs

(The Frescobaldi website is out of date.)

You can download the latest release and get the source code at the Frescobaldi GitHub repository.