PCB is an interactive printed circuit board editor for Unix, Linux, Windows, and Mac systems.
PCB includes a rats nest feature and schematic/netlist import, design rule checking, and can provide industry standard RS-274X (Gerber), NC drill, IPC-D-356 netlist and centroid data (X-Y data) output for use in the board fabrication and assembly process, as well as photorealistic and design review images.
PCB offers high end features such as an autorouter, a topological router and various trace optimizers which can tremendously reduce layout time.
For custom requirements, PCB offers a plug-in API for inserting new functionality and using that functionality from within the GUI as well as in scripts.