You might not think of Apple when you think of servers, but Apple's server line is worth a look. Like its Mac OS X desktop computers, Apple's Xserve line is built on solid Unix underpinnings, with all the stability, power and security that comes with Unix. In classic Apple fashion, the vendor goes a step further and puts it on well-designed, sturdy hardware with features not usually found on x86 hardware, such as remote power on/off/reboot, and built-in hardware health monitoring and alerting.
Finally, it wraps it all up in a user friendly interface.
The Xserve comes on a 1U rackmount quad 64-bit Xeon, which is no ordinary generic rackmount, but designed by Apple. It is a true tool-less design: Every component is easy to remove and replace, and there are no finger-slicing boobytraps or tiny awkward fasteners to lose. Apple has managed to stuff a lot of features into a small form factor: an optional RAID controller, room for a total of 2.25 terabytes of storage, high-speed PCI express, a 256-bit-wide memory controller that supports up to 32 GB of RAM, three FireWire ports, two USB ports, and even a good old reliable for-when-everything-else-fails DB9 serial port. Xserve has built-in support for attaching an external monitor so you don't have to take up an expansion slot, though of course it is designed to run headless like a proper server should. You also get two gigabyte Ethernet interfaces, an optional second load-sharing power supply, and two dual-core Xeon processors.
The three internal drive bays accept either hotplug SATA (Serial ATA) or the newfangled SAS (Serial Attached SCSI). SATA provides maximum storage capacity and good performance at a low cost, and SAS delivers super-SCSI speeds and reliability.
All of this sleek hardware is nice, but it needs software to make it go. The operating system, Mac OS X Server, includes all the basic LAN services: file and print server, network authentication and resource management, netboot server, terminal server for diskless clients, network installation of new clients, Web and mail servers, and a complete stack for application serving. You also get a media server that supports streaming media in several formats.
Included are a number of good system-monitoring and management utilities. An extra-cost option is the Apple Remote Desktop desktop management system, which comes with advanced tools for remote network management.
Mac OS X Server includes unlimited client licenses. That's right, you won't need a special license server just to handle the impossible job of calculating client access licenses, terminal server licenses and various other server licenses it's licensed according to what a server is supposed to do, which is serve clients. Visit Xserve to learn more.