HackEDA is an interesting looking new on-line electronics design tool. The premise is simple: most electronic projects are just electronic Lego: You connect your microcontroller to a sensor, add in a battery, throw in a few caps and resistors for good measure, and hopefully everything will work.
HackEDA takes all those basic building blocks and promises to create a custom Eagle schematic with all the parts your project needs. This looks like a good idea to develop more. Think of it as a mashup tool for electronics: the next time inspiration strikes, there’s that much less between you and the hardware you need to make it a reality.
Here is another somewhat related idea. Script lets you import Eagle boards for use in FreeCAD article tells an idea how an Eagle CAD circuit board design can be imported a proper CAD program in order to design enclosures.
For comparison another interesting idea to handle electronics as building blocks is implemented in Fritzing.