Just as a warning, this is licensed under the AGPL, with a CLA that requires copyright assignment. So, they could pull the rug at any time:

2.3 Outbound License. Based on the grant of rights in Sections 2.1 and 2.2, if We include Your Contribution in a Material, We may license the Contribution under any license, including copyleft, permissive, commercial, or proprietary licenses.

It’s not perfect yet, but it’s much, much better than the old days.

OMEMO is supported by every major client, and they interoperate successfully. Unfortunately, most clients are stuck with an older version of the OMEMO spec. It’s not ideal, but it doesn’t cause any practical issue, unless you use Kaidan or UWPX, which only support the latest version.

All popular clients and servers support retrieving chat history now too.

In practice, I’ve been using it for several months to chat with friends and family, and haven’t had any issues.

I originally suggested Monal to my friend (who is quite into iOS and really appreciates a well designed application) and she found the same, but then she tried Siskin, and was happy enough to use it to this day.

Just for reference, here are my favourites on each platform.

Each support modern XMPP extensions, interoperate very nicely with each other, and (at least in my opinion) look good!

• Android: Conversations
• iOS: Siskin
• Windows & Linux: Dino
• Mac OS: Beagle IM
• Web: Converse JS

As a note of caution, I used Oracle’s free tier to run a personal Matrix server, and it got deleted without any advance warning after a few months. I migrated to another provider and haven’t had any issues for 2+ years now.