I did not join them just for joining them. I am a Racket enthusiast, and the Racket community on Discord is really nice.

There is also a GEB reading server.

The fast.ai server.

Others are OSSU, Rust, MSFT Python, RL group, Yannic Kilcher, sentdex, Eluether.AI, Mark Saroufim's and Aleksa Gordic's ones, wandb, ConwayLife Lounge, Hugging Face, AI Art, etc.