Hubzilla. Closely followed by the intentionally nameless fork of a fork...... of Hubzilla that's colloquially being referred to as (streams).
Perks of both (excerpt):
- not based on ActivityPub, it's actually optional; you can turn/keep it off if you want to
- nomadic identity; my channels are resilient against instance shutdown because they aren't restricted to one instance
- multiple channels = IDs on one and the same account/login; no need to register additional user accounts for this, and you can easily switch back and forth between channels
- OpenWebAuth magic single sign-on, both client-side and server-side support
- very extensive permission settings that let me control what I see, what I don't see and what others can see and do
- per-contact permission settings
- per-channel blacklist/whitelist filter plus per-contact blacklist/whitelist filters plus keyword-triggered, automatically generated, reader-side content warnings, supporting regex and (except the latter) a special filter syntax for extra features
- what's "lists" on Mastodon is actually useful because you can use it both to filter your stream and to limit whom you send a post to, not to mention much easier to maintain
- a concept of conversations, you can follow entire discussions, and you generally receive all replies to a post (something that at least Mastodon doesn't have, by the way)
- not only native support for discussion groups/forums, but they can and do host their own moderated discussion groups/forums (Mastodon has neither)
- no arbitrary character limits, characters only limited by the instance database (on (streams), that's theoretically over 24,000,000 characters for one post)
- probably more text formatting options than your typical blogging platform and definitely more than any microblogging project in the Fediverse
- full-blown blog posts rendered gracefully
- non-standard BBcode tags for special features, often observer-aware
- embedded links; no need to plaster URLs into your posts in plain sight
- images can be embedded "in-line" within the post with text above them and text below them
- no limit on how many images a post can have
- unlimited poll options
- multiple-word hashtags
- post categories in addition to hashtags
- tag cloud plus category cloud/list
- quotes
- "quote-tweets"
- extensively customisable Web UI
- built-in file storage with a built-in file manager, per-file and per-directory permissions settings and WebDAV support that's used for images and other media you embed in your posts (unlike on Mastodon and Lemmy, you know where your uploaded images land, and you can delete them yourself if you need to)
- federated event calendar with support for Event-type objects
- built-in CalDAV calendar server (headless on (streams))
- built-in CardDAV address book server (headless)
- support for OAuth and OAuth2
- modular; can be extended with official or, if available, third-party "apps", widgets and themes
Extra perks of Hubzilla:
- currently more reliable
- more active development
- easier to get new users on board because hubs are listed on various Fediverse sites, and more public hubs are available
- newer and more configurable version of the Redbasic theme
- switchable night mode
- multiple profiles per channel which can be assigned to certain connections
- you can configure new connections before you confirm them
- can also connect to diaspora*
- can also subscribe to RSS and Atom feeds
- event calendar also doubles as a basic frontend for the CalDAV server
- non-federating, long-form articles
- "cards" that work largely the same
- built-in wiki engine based on either BBcode or Markdown for as many wikis of your own as you want to, each with as many pages as you want
- support for webpages (the official Hubzilla website is on a Hubzilla channel itself)
Extra perks of (streams):
- more advanced
- better integration of ActivityPub into the two supported nomadic protocols
- contact suggestions also include ActivityPub contacts
- new default theme in addition to an older Redbasic version
- reworked, more powerful but easier-to-use permissions system
- easier to use once you're on board
- supports BBcode, Markdown and HTML within the same post
- can set Mastodon's sensitive flag for images
- built-in announcement/boost/repost/renote/repeat remover, no need to use filter syntax for that
- extra protection against both mention spam and hashtag spam
- alt-text can be added to images upon upload, no need to graft it into the image-embedding markup code
- verification of external identities (available on Mastodon as well, but not on Hubzilla)