Ubuntu Server GUI is described as 'provides an easy to use set of server management tools designed for Ubuntu Servers'. There are more than 25 alternatives to Ubuntu Server GUI, not only websites but also apps for a variety of platforms, including Linux, Self-Hosted solutions, Windows and Mac. The best alternative is Webmin, which is both free and Open Source. Other great sites and apps similar to Ubuntu Server GUI are cPanel (Paid), ISPmanager (Paid), Zentyal (Paid, Open Source) and Univention Corporate Server (Free, Open Source).
Zentyal is a native Microsoft Active Directory implementation on Linux incorporating all the network services required in a small and medium business environment: Directory & Domain Server, Mail Server, Gateway and Infrastructure Server.
Sentora is an open-source web hosting control panel built specifically to work on a variety of Linux distributions. Sentora is licensed under the GPL and is a separately maintained fork of the original ZPanel project.
DirectAdmin is the easiest to use control panel. DirectAdmin is programmed to be the fastest running control panel available. DirectAdmin avoids downtime by automatically recovering from crashes. We offer lightning-fast support by phone, e-mail, forum, and live online chat.