- Matrix, which has some integration with Lemmy and is the default for secure chat amongst users here who need it.
- XMPP, at least one Lemmy instance is also running it's own XMPP instance.
- Sup, which is explicitly pitched as a Fediverse Facebook Messenger replacement. Now Loops is launched and open source, plus dansup will get a bit chunk of funding via Kickstarter (so he can go full-time), it looks like Sup will be the next one off the production line and will be one to watch.