MisterHouse looks like a powerful open source software package for home automation. Its mainly for getting things to switch on and off according to timers or sensor readings, but some people are hacking it to do more complex things like monitoring heating system performance, which is a good application for environmental and cost-cutting reasons.
It would be a good idea to download the software and play about with it some time. I only wish the documentation was a little more straightforward. So often it’s the documentation and usability that holds back open source projects more than anything else.
Home automation is going to become bigger and bigger business, particularly for reducing energy costs as energy becomes more expensive and scarce. MisterHouse looks like a solid choice for technical types.