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.
For me it's definitely Lemmy. I don't like the microblogging format and never have. I've always used forums and then reddit.
The fediverse just works so well with Lemmy I think. It's so fun seeing new communities from instances I've never heard of. I think this format is perfect for the fediverse