Mastodon - my main social feed platform that first introduced me to the Fediverse in general.
Lemmy - my second main social feed platform that originally substituted Reddit from years ago.
Matrix protocol - communication platform I use to connect with users on the Lemmy instance I'm on
Peertube - would love to get an account going and use it more often but still don't know how but there's FediVideo.
Bookwyrm - Goodreads alternative that I signed up for that could use more work for a genuine reading tracker.
BONUS: my least favorite Fediverse platform lately
WordPress - because I used to run art blogs on there before I heard word about drama about the CEO of the corporation so I basically had to put out my last existing art blog...RIP.
I feel like there's still a pretty big gap in the drawing / art space. I want something that works like the furry art sites all work, which means (a) art posts and text posts separated into distinct feeds, and (b) thumbnails in a grid instead of a vertical timeline. I built a web app to do this but unfortunately it's single-user (and basically locked to the Azure cloud). In the meantime, Pixelfed works pretty well for following Mastodon artists.