A converter of music from Sibelius to LilyPond.
Version 1_01_alpha works nicely even for some more complex cases (e.g., tuplets, grace notes) -- clearly better than what you would expect from an alpha release. Naturally, certain things are still missing. For example, various texts are supported (dynamics, expressions, tempo...), but some less standard are missing. Multiple voices in a single staff are not as nicely aligned as you would wish (tested with Lilypond 2.14) -- notes can be even printed overlapping each other.
The MuseScore project will benefit greatly from this project.