In my case, somewhat chronological order:

1. First Mastodon account, on server that is unmaintained but still running.
2. Funkwhale
3. Mastodon with full name for academic use, on relevant server
4. BookWyrm
5. Kbin (dead now)
6. New Mastodon for hobby interests, as the server of my first account is worthless at this point
7. Piefed
8. Mbin
9. My professional website is in the early stages of federating as well. Still work in progress, but I follow myself and it somewhat works

If a nodebb forum I have an account on decides to federate I might reach double digits.

Edit: I forgot I also have a Pixelfed account! So double digits already.