Errands app (gtk) has caldav support for tasks.

Thunderbird with gnome theme from same developer of Firefox theme for gnome is fantastic. However, I use in my desktop evolution without problems when switching to dark theme.

Mosaicwm is great, even if still on early development.

The installation will fail because it will reboot when trying to remove plasma shell 5. To solve it, I installed with yast plasma 6 addons and breeze style opensuse, because plasma shell with not load after reboot . On my other laptop running tumbleweed also, I decided to do the installation with tty instead of login in plasma and the upgrade worked like a charm.