What is Arduino?
Arduino is an open-source, single board micro-controller with a suite of tools to program and utilize it. The processor can be utilized in electrical circuitry of all types. The Arduino can be used to do anything from simple tasks such as controlling an LED to more complicated projects such as used in a quadricopter or control of a robot. The creators of Arduino have released all the details of the board and its construction under a creative commons share-alike license. Basically, as long as you share your changes to their system, you can feel free to adapt it and reconstruct their Arduino however you wish.