I used to play RuneScape religiously from ~2005-2011. It totally runs on Linux, they even have 3rd party clients that run on Linux (RuneLite). The last time I played about a year ago the game was over run with expensive and unbanable machine learning bots, but using a bot on your own account was almost certain to result in a ban. I spent a few days doing a deep dive into every piece of trivia about RunScape, there was a lot of crazy stuff that went on behind the scenes!

Too bad Jagex sold out to new investors multiple times and overloaded the game with micro-transactions. Their incompetent leadership drove so many players away and then they completely changed the fundamental mechanics of the game in an attempt to attract and retain new players. It didn’t work. They did succeed in wrecking the game so badly, however, that the RuneScape community set up illegal private servers of older versions of the game. Jagex shut those down and eventually re-released the older version of the game themselves which became significantly more popular than the main game.

I don’t play many games anymore, but I’ve been playing Veloren recently. It is opensource and updated a couple times a day right now, the devs are super active and can be chatted with in game.