Lilypond is probably the best free music notator and can face commercial monsters like Finale and Sibelius.
Lilypond is a code-driven editor and can generate PDF, PostScript, SVG, PNG and Midi file simply writing the code in a text editor. If you’re not code-minded, anyway you can use some editors and GUI for Lilypond
After a [...]

One of the best music notation software, good for drums and drumline scores writing, too: Lilypond, with is ascii interface, is definitely a low-carbon software. And it’s free. And it’s complicated, and fascinating. A real good text editor, with pdf preview, tools for macro and template writing, simple parser and other good features is LilypondTool. [...]