All of my fediverse instances in one post:
Fediverse is this complex network of many servers and many services and apps. Mastodon is a large well-formed server that looks like Twitter and indeed if you use halcyon front end, it will really look like you are working in twitter. You can also use pinafore front end to streamline the user interface. For a deep dive, check https://fediverse.party/


Besides Mastodon, there are other services and apps that are worth considering and several of them serve specific purposes. While mastodon, pleroma, and misskey serve similar purposes, i.e, allow text based, photo and video sharing and discussion among the various members of the servers and servers themselves, there are others that are more specialised, although they too, have the social aspects built in. Among them,

Peertube is similar to Youtube
Pixelfed is similar to Instagram
Funkwhale is similar to Spotify (allows music streaming and podcast)
Here are the lists of several instances.

mastodon.nzoss.nz (arin_basu@mastodon.nzoss.nz)
mastodon.social (arin_basu@mastodon.social)
qoto.org (arinbasu@qoto.org)
scholar.social (arinbasu1@scholar.social)
arinbasu1@fosstodon.org
nixnet.social (arinbasu@nixnet.social) This is a Pleroma site
mk.nixnet.social (arinbasu@mk.nixnet.social) This is a Misskey site
Lemmy.ml (arinbasu)
Pixelfed (arinbasu1@pixelfed.social)
Peertube(arindam_basu@tube.tchncs.de)
Funkwhale (arinbasu) Music site
https://audio.liberta.vip/@arinbasu/#channels
Outerheaven.club (arinbasu) Pleroma site