Qiqqa is by far the strongest solution for research and managing pdf's. Zotero, named as a comparison is weak as it does not allow pdf;s to be loaded into its interface - you need to use a pdf reader, which defeats its whole purpose. With Qiqqa documents in a library can be searched together. It has excellent maps of your libraries. It is not prefect, having a few glitches, but still is the only one of its kind.
Sibelius - Sibelius is a virtual score creation tool which allows composers to easily create new piano scores, developed by Avid.
Mendeley - Easily organize your papers, read & annotate your PDFs, collaborate in private or open groups, and securely access your research from everywhere.
MuseScore.org - Create, play back and print beautiful sheet music with free and easy to use music notation software MuseScore. For Windows, Mac and Linux.
Zotero - Zotero is a free, easy-to-use tool to help you collect, organize, cite, and share research.
Finale - Finale, the world standard for music notation software, lets you compose, arrange, notate, and print engraver-quality sheet music.
JabRef - Graphical Java application for managing bibtex (. bib) databases.JabRef · JabRef Help · JabRef | Blog · OpenOffice/LibreOffice .