A really cool open source project that has been brewing for a while is OpenServo. The basic idea was to create a high performance replacement for the guts of standard hobby servos. The clunky RC communication protocol has been ditched for a much more convenient I2C interface, which allows a truckload of OpenServos to be controlled by one master device. That’s great, but the real achievement is cascaded PID control of position, speed, and current. On top of that, the developers have given OpenServo the ability to interpret motion profiles based on a few parameters. The hangup is that the hardware and software design so far is intended to be used with hobby servos only, which get position feedback from a cheesy potentiometer instead of a quadrature encoder. If quadrature encoder support was added (and I believe it is in the works), the hardware design should scale up really well for larger motors. The software is already to a point that would make it useful for a wide variety of applications other than small hobby servos. This should be a great project to follow.