It all starts with the schematic. I use KiCad to design the schematic and the PCB. KiCad is open source and available on Windows, Mac OSX and Linux.
I use it on a Windows 7 machine, and occasionally on a Macbook pro.
I use a fairly recent version, (build BRZ 5376) and found it superior to the "stable"build.
Nothing revolutionary going on here. A ATMEGA328, with most of its pins broken out. There is a 6 pin header for the In Circuit programmer.
Notice that there are 2 crystals
One is the PTH version, and one is the SMD version. In the design they fit nice on each other, so the user of the board has can choose either version.
The same applies to the reset switch. There is room for a PTH and a SMD version.
There are also PWR_FLAG on the power lines. That is a thing of KiCad. When doning a DRC (Design Rule Check) KiCad complains that the power lines are not fed with juice. By putting the power flags in the schematic, KiCad DRC stops complaining.
The pin out follows the "Arduino convention". Most of the time I put the Arduino bootloader in the chip, and use it as a Arduino clone. More on that later.
This is how this part of the schematic looks on the pcb:
Stay tuned, more to come