First, an operating system is needed. There are a couple of ways to go, but certain prerequisites should drive the choice. First, a successful server appliance should be a "headless," meaning the unit will function without a monitor, keyboard, or mouse. Those components will be needed for the initial setup only; after that, the server appliance will be managed by a browser from another, network-attached system.
There are a few OS choices that can be used to roll together a server appliance. First and foremost, there is the server appliance development kit (SAK) from Microsoft. Unfortunately, that product requires a system builder to become an authorized OEM.
Next on the list of choices: a Linux distribution. A system builder will find all the pieces there to build a successful server appliance. But they will have to invest the time and effort into arranging the various software components into something useful.
With those concerns in mind, a system builder may want to pick a pre-configured OS for a server appliance. There are several on the market. But a system builder will probably be best served by a server suite, such as NetMAX Professional Suite from Cybernet Systems, an independent software developer.
NetMax Professional, now in version 5, is built on a Red Hat Linux distribution and includes the following features: complete Linux server environment, browser-based GUI, DHCP server, DNS server, Internet sharing, extensive reports, mail server, ftp server, Web server, Web proxy, VPN server, and more. As you can see, the list of features is extensive.