MUDs. Text based (generally RPG) games with incredibly immersive story telling, near infinite levels of character customization, and many even feature ways for players to build on the world itself.

I’m surprised it’s not more popular amongst D&D enthusiasts.

In its hey day, people spent thousands of dollars just to boost their characters on massive for-profit MUDs like those created by Iron Realms. But smaller MUDs like Ancient Anguish were just as quality.

Sadly they’re going extinct. Only a few MUDs are still actively maintained.