DC Denison of MAKE says:

Autodesk today expanded its suite of free 3D tools by partnering with Circuits.io to launch an electronics design tool: 123D Circuits.

The program allows users to create virtual breadboard-based designs to build and experiment with circuits. A virtual Arduino board can be added to the design, and the code can be edited in a browser window and simulated. The code can also be edited collaboratively (“a Google Doc for electronics” Autodesk claims).

The program also provides hooks that allow users to have the virtual boards professionally manufactured.