@Longicaudatus

Web 1.0 was definitely a different experience. If you're looking for something old school and in the same vein as Pixpet, my brother recently showed me Telefang.net, a site and community surrounding an obscure series of monster-collecting games for the GBC/GBA. I don't actually know what the community is like since I only glanced at the forums, but if you want to play the games themselves, you'll probably need an emulator. I've been meaning to try them myself. There's even a completed manga for the series.

As a kid in the early 2000s I used to play a lot of 2D multiplayer games on a site called BYOND, which looks the same as it ever did lol. All of the games there are free and user-made, so they vary in quality and completeness. As a result, the community consists mostly of hobbyist coders, pixel artists, and the people who follow their work. There's also a ton of fan games if you're into that. The only drawback about BYOND games is you have to download their client to play (desktop only).

I'll let you know if I think of any other ancient sites/communities that still exist XD