What is the Archive.org? It is the website for the not-for-profit organisation known as the Internet Archive. It was founded in 1996 and located in San Francisco.
The Internet Archive is really about storage and preservation of the internet and digital data. The Internet Archive downloads, indexes, and stores just about every website ever made on a periodic basis. This service is what they call the WayBack Machine (http://www.archive.org/web/web.php) and you can access its archive very easily. It is a useful tool for seeing older versions of your website, or for checking the content webpages that have gone offline.
You can also subscribe your organisation to one of the internet Archives services call Archive-IT (http://www.archive-it.org). This service enables you to archive and preserve your organisations materials using online tools provided by the service.
In addition to this the Internet Archive makes available storage space for free for just about any data you may wish to upload. You can store software, video, text, audio, you name it. There are some small requirements, the most obvious being that you should own, or have clearance to contribute, the works. You must also license the work under a Creative Commons (or similar) license. This is usually not a problem if you made the work yourself, but maybe an issue if you used copyrighted material (eg, music within a video) within your work, or you are uploading something someone else made.
The Internet Archive is very very useful and will become more more important as a historical resource as time goes by.