As more and more great music slips into the public domain, and as documents move more freely than ever from person to person by way of the internet, the Petrucci Music Library grows larger and even more interesting by the day. The number of scores, as of yesterday, is 38,000. That's a lot of music.
This Library, which is part of the International Music Score Library Project, gets contributions from libraries, librarians, and musicians around the world. There are complete sets of orchestral parts to download, pieces of chamber music by well-known composers that I never knew existed, and a lot of music by excellent composers from the 18th, 19th, and 20th centuries that I have never even heard of before. There are forums (in four languages) that discuss everything from copyright to musical analysis.
There were so many scores published on cheap paper during the late 19th-century and early 20th-century musical feast in Europe. Many are in such fragile shape that they are not allowed to travel out of their isolated homes on a handful of library shelves that are scattered around the world. Thanks to the people who manage this project, they can be downloaded here, and you can print them on good acid-free paper, giving them another life. You can play them. You can record them. You can share them with friends and students. You can study them.
The eventual goal of the Project is to create a virtual library of everything in the public domain. Now if that is not a significant contribution to the musical world, I don't know what is.