PCB is described as 'interactive printed circuit board editor for the X11 window system' and is an app in the Education & Reference category. There are more than 10 alternatives to PCB for a variety of platforms, including Windows, Mac, Linux, Online / Web-based and Android. The best alternative is KiCad, which is both free and Open Source. Other great apps like PCB are Fritzing (Paid, Open Source), Autodesk EAGLE (Free Personal), OrCAD (All Products) (Paid) and Altium Designer (Paid).
The gEDA project has produced and continues working on a full GPL'd suite and toolkit of Electronic Design Automation tools. These tools are used for electrical circuit design, schematic capture, simulation, prototyping, and production.