I keep meaning to do something with my Neocities account, and then I don't.

Browser-specific tags for animating text: If I recall correctly, Netscape allowed "blink" and Explorer allowed "marquee" and nobody cared about Safari because that was the period in between Steve Jobs ruling holding the CEO position at Apple and Macs were awful and the iPhone didn't exist yet.

Sites having the most incredibly gnarly and boring mobile versions, because if you were online it was with a Blackberry from work.

Embedded midis.

Web rings!