Lots of these kind of products out there. RoboFocus by Home Dome, JMI's Smart Focus, and then there's several others I remember coming across in my searches a couple of years back.
I use RoboFocus on my JMI NGF-C. I think it used to be that the RoboFocus was a stepper motor so could accurately go to an exact step/location, where as the JMI one was a servo motor so didn't have the same level of repeatability. I could be completely wrong, it's been quite a while since I compared them, but that's something to watch out for.
I control the RoboFocus through the computer where it has all the advanced controls you'd want - go to exact position, move in/out by x amount, temperature comphensation, compatability with Ascom and hence lots of other pieces of software such as FocusMax.
I once did a bit of a write up on it, I have no idea how relevant it now is, it's been years:
http://www.rogergroom.com/rogergroom...em.jsp?Item=65
Roger.