You're supposed to self-host it (or rent a hosted instance). But rather than having open registration (or creating accounts beforehand and sending the credentials), you generate invites and send them to your contacts. The invites onboard the users to install the app.

The Snikket client works with any XMPP server, and the Snikket server works with any XMPP client.

The Snikket clients are soft forks of existing clients. The reason of their existence is having consistent branding.

In fact, I recommend using Monal as an iOS client instead of the Snikket iOS one.

Note: you can set up invites on any regular Prosody / ejabberd server.

https://prosody.im/doc/modules/mod_invites

https://docs.ejabberd.im/admin/configuration/modules/#mod_in...