DipTrace
DipTrace is an advanced PCB design software application that comes with PCB Layout module, powerful auto-router, Schematic Capture and Component/Pattern editors to design your own component libraries. Besides being very simple to learn, which is quite an accomplishment for an engineering... Another important features are Design Rule Check (DRC) and Net Conectivity Check - the functions that check the clearance between design objects, minimum size of tracks and drills, which ensures board accuracy, and connectivity of all nets not depending on how they are connected (with traces, thermals...
http://www.diptrace.com/downloads/diptrace_en.exe - 16Mb - Download - Screenshot

DipTrace Free
DipTrace is an advanced PCB design software application that comes with a PCB Layout module, a powerful auto-router, Schematic Capture and Component/Pattern editors to design your own component libraries. Besides being very simple to learn, which is quite an accomplishment for an engineering... Smart manual routing tools allow users to finalize the design and to get the results they want in a blink of an eye. ... A net connectivity check allows you to check all electrical connections and find all broken nets and their isolated areas.
http://www.diptrace.com/downloads/dipfree_en.exe - 16Mb - Download - Screenshot