I still advocate for IRC. There are some really long running communities that are absolutely solid in my opinion. Maybe I'm just getting old but I find the discord structure and eco system to have too much chaos and trolls. Not all of course.
`/list` This will list all, but you can filter for min people for example in the channels
`/list -min 10`
But over the years of being on IRC and growing list of communities and friends I have a few that I join for particular areas of interest but as for an all in one 'directory' I'm not too sure if one exists.