The Internet Archive is an extremely valuable resource for researchers and the general public.
Out of print books, music, and software are only a portion of the materials available for free from the San Francisco based website. Perhaps one of the most popular features is the Wayback Machine.
Simple enter the URL or web address of a website, and the Wayback Machine will provide you with the ability to view the website as it appeared months or even years ago. (Assuming the website in question was active and allowed for archiving, of course)
Looking for an out-of-print book from the 1800’s? With over 8 million books in the archive, there is a fair chance you will find it.
The Internet Archive was founded in the 1990’s, and has steadily grown in popularity, funded by a non-profit private foundation and donations.
Dive in and explore. There is something of interest for everyone.