Arduino is the official name for an open source micro-controller hardware technology developed in Italy. The boards are available fairly cheaply and there are sensor, motor, communication and other hardware add-ons available. They have been adapted for many purposes. See the handout from an Arduino training course from http://www.sparkfun.com for some great references.
Tcl/Tk seems ideally suited as a programming languages for this technology as the interface to deliver code and i/o to the microcontroller boards. What a great new future for tcl as a Tool Command Language for actual tools as well as software tools. (But wait! According to Linuxcnc.org , Tcl/Tk was used for the interface to early CNC equipment at NIST . It is still used as an interface to EMC2 in a software called Axis .)
There are a few projects noted around the web: