I am a Crestron authorized independent programmer, which essentially means I write customized programs that can be used to control an entire system at the push of a button, these systems can comprise of anything from your AV system in your lounge to, lighting, air conditioning or even the hot tub. The above would be an example of my residential target market.
In the commercial industry, I would for example, write a programme to control a projector in a lecture theatre, the audio level for the presentation, the video conferencing and even the lights, all at the push of a button.
My clients range from integrators (audio visual installation companies), consultants, architects, building contractors, end users and even the odd buddy or two.
Not only do I write the tricky code that makes all the different devices in a system work, but I also design the GUI for the touch panel (well I don't do the graphic design as such, I take already made templates and arrange them to suite a particular job).
Here is a link to the manufacturer who's products I use to control these systems with, it may give you a better idea of what it is that I do.