KiCad is a popular open source printed circuit board layout program that runs on all three major desktop OS's (Windows, OS X, and Linux). It was originally written by Jean-Pierre Charras at Université Joseph Fourier and is now actively developed by an enthusiastic team of developers. KiCad is quite capable of producing production-quality designs and has been my EDA tool of choice for several years.

Like all PCB layout programs, KiCad has a steep learning curve. So here's a few things that I am hoping might help ease bits of the curve.

• Schematic symbol management
• PCB footprint management
• Some best practices

• Quick guide to using KiCad for SPICE simulation
• Using arbitrary SPICE engines in KiCad 5

• Stitching Layers Between Copper Zones

• Introduction to PCB Design Tutorial (featuring KiCad) video series
• PDF output from KiCad in Linux

• PCB modules :: LGPLv3
• SPICE components :: LGPLv3

• KiCadLib.org :: Licensing varies?
• Open Source Hardware Engineering Community :: Ported from Eagle; apparently not free.
• http://smisioto.no-ip.org/elettronica/kicad/kicad-en.htm :: CC-by-SA

• C. Rohrbacher's component (online) and module (online, beta) generators.
• Robert Fitzsimons' footprintbuilder (Java, GPLv3)