Thanks for testing Maegios!
My guess is that the app can't properly connect to your Nagios instance due to incorrect URL and/or username/password. Make sure that URL has "/nagios" appended to the end (or the location where you go to when accessing Nagios through a web browser).
There was a bug introduced in the last release that keeps showing "fetching..." instead of "Disconnected" when Maegios is launched by clicking the widget and can not connect to the Nagios instance. It will be fixed in the next release and more specific messages will be added on top of "Disconnected" to aid with initial configuration.