Eagle
EAGLE is the well know CAD application for designing PCBs.
https://www.autodesk.com/products/eagle/free-download
Hackaday Tutorial
Part 3
Packages
Sparkfun library for many common parts (https://github.com/sparkfun/SparkFun-Eagle-Libraries) ¨
IAD library https://github.com/IAD-ZHDK/IAD-Eagle-Library
Design Rules
Use Sparkfun Rules as default (https://github.com/sparkfun/SparkFun_Eagle_Settings)
Draw 32mil wires
Change Clearance also to 32mil
Ground Plate
Draw a Polygon around the PCB
Select Info and Set Isolate to an appropriate value
Select "Ratsnest" from the Toolbar to calculate the ground plate