In the past, we've talked about the Mac Mini as a media server. Now Mundy.org has an excellent three part series that shows you how to set up a low cost home automation server using a Mac Mini. The article gets you started with:

We're going to build this system using X10 technology so you need some software to control the timing of home automation tasks and to send X10 signals over the existing electrical wiring in your home. These signals control turning lights on and off as well as dimming them. And they can control appliances and thermostats. Combinations of tasks can be sent from the server to dim the lights, turn on your home entertainment system, choose a playlist from iTunes, and draw the drapes. It all depends upon how spiffy you want your ultimate system to be. Now that you have your Mac mini, the next required component is the X10 control software, an extremely powerful, well-supported product called Indigo. It costs $89.95 and is available with a 3o-day free trial directly from the author. Next, you'll need a PowerLinc USB device, which is the device to which Indigo sends device instructions at scheduled times specifying when particular events should occur (e.g. driving in the driveway, sunset, or two hours after no motion is detected on motion sensors #1, #2, and #3). The PowerLinc device then sends the actual X10 signals down your power lines to individual X10 devices which control each light, or appliance, or outlet in your house .

This is an excellent tutorial if your looking to get started in home automation.

Read The Ultimate Home Automation Server: Your Shiny, New $500 Mac Mini