There are many CAD developed to assist the electronic designers during drawing of PCBs and schematics; often they are integrated in complete suite to project, simulate and realize a whole electronic system. Besides the many commercial versions, there are also free CADs available. Today we’d like to analyze one of the most diffused and known software: Eaglecad (eagle does not mean the powerful bird but it is the acronym of Easily Applicable Graphical Layout Editor) made by Cadsoft, actually at version 6.2.0. We have chosen this one because, as you know as an Arduino’s fan, the official pcbs and schematic files of the boards are developed and available free of charge to everybody in Eaglecad format; you can find also a lot of libraries and circuits made by famous DIY website (Sparkfun for first) available for free.
How to make an Arduino shield with Eagle CAD - [Link]