This page can help you find reliable, scholarly editions of printed music online that have been created by musicologists. The resources collected here are not meant to be an exhaustive list or guide to online music editions, but rather a selection of reputable tools to help you identify and locate online music editions yourself.
These sites only list various online historic sheet music collections, but do not search them.
These collections generally include popular music (piano and or piano-vocal pieces) from the mid-late 1800's to the early 20th century, but scope varies by collection.