Although the Arduino development platform may seem somewhat simple, with a little imagination, the right parts and some clever coding you can reproduce all manner of complex devices. This has been demonstrated very well by Sebastian Hirsch with his Arduino-powered ultrasonic scanner. By mounting an inexpensive ultrasonic distance sensor on a rotational servo, distance data around the point of rotation can easily be taken for all angles.
This data is then processed by an Arduino and sent back to a PC running code based on Scala and Java. This interprets the data and displays it in a typical "radar scree" type of form. The system is not totally accurate, in that the sensor can only detect the closest object in each measurement - and a rotatational speed calibration is required after every system reboot. However it works well and could be a lot of fun, as demonstrated in the following video: