According to FediDB, here's the software user distribution of the Fediverse:
Mastodon - 78.0%
Misskey - 6.2%
Lemmy - 3.3%
PeerTube - 3.0%
Pixelfed - 1.8%
Pleroma - 1.5%
Microdotblog - 1.2%
Writefreely - 0.7%
Kbin - 0.6%
Other - 3.7%
One service that isn't mentioned is Diaspora which, with 670,000 users, would actually be the third largest service on the Fediverse. The reason why it's not mentioned is probably because Diaspora uses its own protocol instead of ActivityPub. However, certain ActivityPub-enabled services, such as Friendica and Hubzilla, can communicate with Diaspora.
We should also keep in mind that Bluesky with AT protocol exists, but since it hasn't federated yet, it wouldn't be fair to include it. This applies to Threads as well -- it still hasn't implemented ActivityPub.
All in all, the noteworthy update is that Mastodon's share of the Fediverse is gradually decreasing. Around this time last year, it composed almost 90% of the Fediverse.
