The World Wide Web. The reason that web site addresses generally start with "www". The graphical, easy-to-use interface of the Internet. Seems like it's been around forever, right? Well, not really.
Actually, it's only been around for twenty years. In celebration of its 20-year anniversary, the European Organization for Nuclear Research (which, for some crazy reason is abbreviated as CERN), has re-published the first web page ever. I've enclosed a screen shot, but if you want to see the actual page, click here. (WARNING: It's not very sexy.)