I had replied to a post on Threads with the following info, but I'm in the process of deleting my content over there, so this seemed like a good place to stick it for now 😄
* Twitter/X, Facebook, Instagram, & Spoutible are commercial & centralized
* Threads is commercial & centralized, but can access Fediverse (ActivityPub)
* Bluesky is commercial & decentralized (AT Protocol)
* Mastodon is non-commercial & decentralized (ActivityPub Protocol)