Legatus is an AES encryption supported chat room.
It cannot do much for the time being and is just a basic chat app. Host the python flask server and set it's URL in the source code and then build. I suggest hosting it on replit and keeping it up with UptimeRobot if many people won't be using it. It can be further modified to work like a fully fledged chat app like WhatsApp or Telegram.
Download and install one of the .msi releases.
After that, open Legatus and click the top right options icon.
Then type in the URL of your hosted server(or try using my test server: https://legatus.teslestien.repl.co/), any username of your choice and a background image if you wish.
Ask your friends to join and enjoy the secure communication.
The test server can be publically accessed so do not use it to share sensitive information.
For changing the encryption key you will have to change it in the source code and build your own release because the encryption key used by all the users in each release should be the same.