>One I don't know very much about is Kissu. I think it's been around for a while, but i have no idea how it came about, nor what it's been doing.
They have a FAQ:
https://kissu.moe/faq
>What is Kissu?
>Kissu is an imageboard created by Verniy and Cool-Guy in 2018 with help from users who left 4chan's /qa/ board. It uses a custom-built user interface inspired by CCD0's 4chanX extension running on top of a heavily modified Vichan engine. It hosts a variety of Japanese themed content and strives to keep it easy.

I don't want to get too much into it since it involves a lot of Rule 8 garbage, but basically kissu is made up of the anime/otaku crowd who used to gather in /qa/ (treating it as some type of "2D/Random" board - 4chanX even renamed the board to that by default in response) before it was taken over by the s*yjak spammer crowd (who later also moved to their own sites)