The Internet Archive maintains historical snapshots of the web. For many years on the web, when a web page was taken down it was lost forever, often unexpectedly. However, now you can turn to Archive.org and its database of old web pages to retrieve a lost page if it was around long enough to have been indexed.
The Internet Archive is a public, nonprofit U.S. corporation founded in 1996 to build an Internet library with free access to researchers, historians, and scholars. It provided shell level access until 2001 when it added a convenient web based interface called the Wayback Machine, immediately making it widely available to everyone over the web. The site also maintains a set of historical Usenet newsgroup and FTP archives.
The Internet Archive is located in Presidio, California, appropriately founded in the 17’th century by Franciscan Friars. It also collaborates with several educational institutions, including the Library of Congress and the Smithsonian Institution.
The site Alexa.com also maintained a database of web pages which it made available to The Internet Archive, and now provides a web browser add-on that provides a range of information about each web site you visit.