An Arduino board can do many things, and Didier has described in detail methods for measuring extremely low frequency electromagnetic fields using just an Arduino board, some wire and a few special libraries.
You could also display the results using a grapic LCD unit to make a portable version of this simple test equipment. For more information, descriptions and the Arduino sketch, visit Didier's blog. To get started with your own measurements, consider our Freetronics LeoStick - one of the smallest Arduino-compatibles on the market which also includes an onboard RGB LED and piezo buzzer:
