What Is Arduino For: Robots!

Arduino: Robot Board
What Is Arduino? Arduino is an open-source ROBOT platform, it is "easy" and flexible, of course it's not easy at all - unless you already know about electronics and open source platforms, and even then — like all open source projects, you'll have to map out a mesh network of forums, irc channels, blogs, tutorials — learning about how it's fragmented over the years — which is a 3rd party product — which is true to the ideology of the original Arduino. But Enough whinging because it IS actually really cool.
Arduino is an open-source single-board microcontroller, descendant of the open-source Wiring platform, designed to make the process of using electronics in multidisciplinary projects more accessible. The hardware consists of a simple open hardware design for the Arduino board with an Atmel AVR processor and on-board input/output support. The software consists of a standard programming language compiler and the boot loader that runs on the board.  Wikipedia
If you don't understand all of that don't worry  it's just nerd gibberish for "Arduino is a DIY circuit board for making cool home made robots* (*but you will have to study a little bit)" Arduino is not just the board though, it's also the software that controls it, of course it's open source and cross platform (windows osx and linux).

Here is a very cool robot made with an arduino: