[mistermann]

Some of them are listed here:

https://theportal.wiki/wiki/The_Portal_Discord_Servers

The CoffeeHouse is probably a good place to start as it's a bit of a main hub, and over time you will get invited to other ones.

Fair warning though, there is a significant amount of religion/spirituality, psychological woo woo, ironic overconfident naivete, etc. Not really all that different than you'll find in any community consisting of human beings, but the flavor and magnitude in these communities is likely quite distinctly different than what the HN culture is likely familiar with. They could sure use some more strictly rational people, and they definitely need folks with advanced technical skills, particularly programmers.