The Virtual Appliance comes in the OVA virtual machine format with a preconfigured GNU Gatekeeper plus web interface.
The Gatekeeper is configured as a H.460 NAT traversal server and you can assign it a public IP through DHCP. You simply start it in a virtual machine and give it as much hardware resources as your call volume requires. It doesn't have any artifical limit on the number of calls or registrations it can handle.
Datasheet: Supported standards
The appliance can be imported into various virtualization solutions, eg. VMware, VirtualBox, Xen etc.
If you prefer other containers, eg. Docker, please contact me.
Price: 590 Euros (license for one instance)