Piefed is another instance type that is growing in popularity, and a few instances are now turning on the API. As such, apps are also implementing support.
It would be great if Boost would support it too. Hopefully the extra development overhead isn't too bad.
Some recent discussion: https://piefed.social/post/817564
The page for developers:
https://join.piefed.social/docs/developers/
The API for third-party apps (frontends, bots, etc) is 95% the same as the Lemmy API.
That same link: https://freamon.github.io/piefed-api/
Like Matodon Piefed also steps outside ActivityPub to do stuff its own way, which is not a good thing IMO as you end up with fragmentation.
None the less, I am trailing piefed but find the Interstellar app annoying... so.