I've installed 3 Chatmail clients on my phone today (I think Chatmail is the name of the protocol, but everybody calls it Delta Chat, but then Chatmail doesn't present itself as an interoperable protocol either, it presents itself as a collection of software projects and it's unclear whether Delta Chat is part of it or a spin off):

- Delta Chat
- Arcane Chat
- WhatsDown

The 3 are basically the same app. I didn't check but they probably share 99% of the codebase. I don't understand.

Also they allow you to share an invite link for others to talk to you, but I couldn't take the invite link from one and paste on the other because there is no place to paste, only a place to read a QR code.

It's not clear whether I'm supposed to share this invite link publicly or if it's a private thing for only one person to message me (the invite link is big and full of metadata in it). If it's private how am I supposed to send it to someone, using another messaging app?

Also apparently they create accounts for you in a random chatmail server, or Delta Chat at least seems to do that, while Arcane Chat seems to always use arcanechat.me (or something like that), so that could be the reason why they have different apps that are almost exactly the same: the hardcoded setup parameters.