The internet is constantly changing. It’s rare when a site stays the same for years — far more often, sites change so often that you almost can’t rely on older links at all. It’s a terrible problem for citing sites in research papers, and an even worse problem for historians and geeks who’d like to look back at the beginning of the internet, since it’s largely already disappeared.
That is, it would have all disappeared if the Internet Archive wasn’t around. This ambitious non-profit project aims to build the definitive internet library by snapshotting much of the crawalable web and makes it available for anyone to sort through in the Wayback Machine, among other projects. It’s an incredible tool to look back and see, say, how Apple.com looked in ’98, and it just recently got a facelift and an API that makes it even more useful.