The GNU Gatekeeper is free and very powerful. If you want to make your life a little easier, you should buy the web interface to have a graphical interface to configure and monitoring the GNU Gatekeeper. You'll be able to see ongoing calls, registrations and some statistics.
The web interface can be used from a desktop web browser as well as on mobile devices. It uses a responsive layout that adapts to your screen size.
The interface runs on a PHP enabled webserver on the GnuGk server (tested with Apache and IIS and PHP 5.x and PHP 7).
Please try the online demo (user name "demo", password "demo").
Price: 200 Euros
The web interface works best with GnuGk 4.0 and above, but you can use it with any version down to GnuGk 3.1 if you don't want to upgrade, yet.