[arianvanp]

Yes there were many. This is how I got into programming in 2006. The fact that OSRS even happened is because Jagex was losing a lot of people to private servers.

I've been out of the community for 1.5 decades now but there (used to) be a thriving private server community at https://rune-server.org/index.php which shaped my entire programming career

Whether there are still actively maintained ones I'm not sure though.