Element is a personal messaging program which uses Matrix protocol: https://element.io/
Matrix https://matrix.org/
Install Element desktop through Pacman:
sudo pacman -Syu element-desktop
You can now run it with element-desktop.
You can create an account on matrix.org by default, but you can later change the homeserver to some other and your account should be transferable!
You can also access web interface here (used as a default on the confirmation email): https://app.element.io/#/login