Here’s an interesting project which aims to create a low-cost digital servo for robotics -
“OpenServo is an open community-based project started by Mike Thompson with the goal of creating a low-cost digital servo for robotics. The hardware and software design of the OpenServo is free for anyone to use and modify to meet their particular needs. It is currently being developed by a small group of dedicated individuals striving to maintain the very best in free, open source software and standards. We hope that you will find the OpenServo project interesting and become a member of our community.