We can remember when all this was HTML2
Beneath the average web site, where you're generally not looking, there are lots of different technologies all playing along with different browsers to hopefully make everything work nicely and look attractive. And although the web hasn't really been around that long, the mix of technologies has changed a lot since Tim Berners-Lee posted the first web page.
The Evolution of the Web visualises this gradual change in timeline form, tracking technologies and browsers from 1990 through to the present day. There's a rash of new stuff in the early days, then a strange bit between 2000 and 2003 where not much happens at all, after which the various elements of HTML5 start to appear, slowly at first before really kicking off around 2008 and set to dominate everything by next year.
It's a lovely little visual history of the web, complete with plenty of nostalgic screenshots of all the major browsers. Remember Mosaic? It would throw a fit if you tried to look at this page on it.