I recommend Delta Chat, it doesn’t needs to create an account since it is just an email client with a chat interface, it is not a replacement for your fancy chat app but for your email app, everyone have email, so will need an email app anyway, it makes email easy to use and encrypted out of the box without your friends having to know what encryption means.
I like XMPP but UI/UX is really poor, it is surprising that this email client has a much better UI/UX than Conversations, it has swipe to reply, etc. I found Conversations ridiculously “hard” to use, blabber.im improves a lot of small details that have an impact in the users every day workflow
it is an old reply, but for the new readers: system tray was implemented time ago, the desktop version has improved a lot,
it is not imitating WhatsApp in particular but a messenger app, and that is the whole point of the project, being a “chat by e-mail” app, a new approach to managing and displaying email, if you prefer the classic inbox clients then just use them, you don’t have to use Delta Chat to communicate with other Delta Chat users the same way you don’t have to use Thunderbird just because your peers do