FreePCB is a free, open-source printed circuit board layout editor for Microsoft Windows, released under the GNU General Public License. It is not quite finished, lacking some important features such as a Footprint Editor, Design Rule Check and Autorouter. However, it is quite capable of laying out a PCB and producing Gerber files. Some of its features are:
– 1 to 8 copper layers
– Board size up to 60 inches by 60 inches
– Footprint libraries courtesy of Ivex Design International Inc.
– Copper fill areas
– Imports PADS-PCB netlists
– Exports extended Gerber files (RS274X) and Excellon drill files
If you use FreePCB to design a PCB, I would STRONGLY suggest that you check your Gerber files with a program such as ViewMate (available for free here) before spending any money to have the boards manufactured.