|Someone is wrong on|
The Internet Archive is a US non-profit organization and the website it runs. As the name suggests, it is a massive archive of digital text, sound, music, video and even software and webpages. Most of its content (except webpages) is either public domain (e.g. its copyright has expired or it has been created by the US government) or under a free license such as Creative Commons.
All of this means that in it you can find rare songs, obscure archive footage of nuclear explosions and... Moon landing denial videos. Of course, the Zeitgeist movie is also on board, in several different variants.
Their headquarters is in a former Christian Science church, which earns them even more coolness points in RationalWiki's books.
 The Wayback Machine
The Internet Archive also runs "bots" that crawl the Web and save archive copies of the pages they come by, similar to the way search engines like Google create their search indexes. Not all pages are crawled and even if a page was archived, nothing guarantees that the archived text covers all revisions to the page or the one you are looking for. The Archive's bots honor the robots.txt[wp] files, which means that they won't crawl stuff that the owner of the website doesn't want crawled. They also retroactively hide sites if the current robots.txt forbids crawling and take down page archives by the original owner's request. So, don't rely much on the existence of their copies.
The Wayback Machine is the name of the subsection of the site that serves as an access point to the web archive. Just enter an URL and go.