The Choral Public Domain Library includes free choral and vocal scores, texts, translations, and other useful information.
The contents of IMSLP include searchable scores and recordings that are in the public domain.
The Open Library is an open, editable library catalog that is building toward a web page for every book ever published. Electronically available scores, books about music, and more are included.
A digital presentation of over fifty chant manuscripts (e.g., antiphonaries, graduals, processionals, etc.) containing music intended for use during the rituals of the Roman Catholic Mass and Divine Office.
The Mutopia Project offers sheet music editions of classical music for free download. These are based on editions in the public domain. The project also offers a growing number of modern editions, arrangements, and new music. The respective editors, arrangers, and composers have chosen to make these works freely available.
Scores and books in the public domain. Many of these are unique to the Sibley Music Library collection.