Zello enterprise server is a standalone Zello server, which you can install at your organization (i.e. behind corporate firewall or into LAN). If you don't require the closed-loop scenario, you may consider ZelloWork product, which is basically a hosted version of Zello enterprise server.
Use web-management console to control users, channels, access rights and software updates within your organization or integrate with your systems using Zello server API.
Software gateway option enables interoperability between your exisitng radio or public announcements network and Zello.
Zello SDK allows you to integrate push-to-talk into your existing applications using ActiveX technology.
Zello client app runs on various platforms and Zello enterprise server software runs both on Windows and Linux.