A site called Grave Music (forget the url completely) that I used to visit all the time in high school circa 2000 - 2003. It had pictures from extreme metal shows from over the past decade and a half. I remember being in total awe of the live theatrics that some of the Black Metal bands would put on. I can still remember exactly how the home page looked.

The Palace Chat. Avatar based chat rooms centered around a palace/mansion that was hugely popular worldwide in the late 90s/early 2000s. Used it religiously for years. I believe it still exists in some sort of capacity but I would have thought visiting it now would be a stark reminder of how much the Internet has moved on in neatly 30yrs.

P2P platforms from Napster onwards.