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Kicad - pcb cad software
True open-source. UI based on wxWidgets, so it runs natively on Windows, Mac and Linux. From the look of some of the example boards that come with the download, it is clearly capable of very complex layouts. It also seems to have rather nice library mamagement facilities too. Finally, it does seem to have attracted a fairly active development group. It's the sort of SW I'd expect to be fairly popular in the OSS community - very technical and appealing to academics. It's clearly advanced very rapidly over the past few years.