[Tepix]

Where do people play nethack online these days?

There's a list of public servers in the wiki at https://nethackwiki.com/wiki/Public_server but it's hard to tell at a glance which ones are most popular.

em.slashem.me has an SSL certificate which expired last April.

[raspyberr]

I think nethack.alt.org has the most players but what I've noticed is that hardfought.org has a much chattier community on IRC.

[bhaak]

And Discord. Some of the NetHack IRC channels are bridged with the RL Discord.

https://nethackwiki.com/wiki/Libera#.23.23nethack-discord