this part is actually a bit harder, since many communities, come and go... I do feel like those apps create their own communities, of the people who use them, but I know what you mean... this is the first one I can think of that I know is active:

Hive account@creativesteem - "Creative Community Collective - Contest Central & Steemian Artist Promotion - Exclusive Reward Fund & Investment Initiative"

and of course slothicorn :) which is similar to creativesteem, but specifically for cryptocurrency related art in the creative commons.

There is the writers block, which is a community of professional writers, or writers apiring to be professional writers. They have mentoring, workshops, and peer review processes. https://discord.gg/WRdJBQT

There is the You Are Hope community, which is quite possibly the most successful charity initiative on steem https://discord.gg/hWDRQUY

The Babel-Pond which is a collective of translators, who work within the steem comunity https://discord.gg/cjxYZkH

Hive account@cervantes connects people in the spanish speaking community... there are many discord communities... but I don't have the most current list of them at the moment, so I'm struggling with this part.