The Wayback Machine is an archive of the entire Internet, or as much as the non-profit organization "Internet Archive" can provide.
If you are trying to find information on a website that you know was once there but your link is now broken, you may be able to retrieve it using this free service.
See also the Library of Congress' Web Archive Playback Service, which is attempting to do something similar (as of Jan 2025 is still in "beta").