Fen Logic Ltd. Gertboard:
The Gertboard was the very first expansion board for the Raspberry-Pi. Development and prototyping was all done in-house. The final production was done by a retail company, in cooperation with their own manufacturing plant on a royalty basis.
The board was meant as a first step for programmers to get familiar with hardware and writing code to interact with it. (For some reason somebody can write a beautiful fractal program and find the result 'booooring'. But lighting a single LED using the computer makes them enthusiastic).
Before any hardware was developed, a learning plan was made which takes the user step-by step through the very first stages of talking to the outside world: For that same reason more then normal effort was put in the manual. To stay in the educational spirit of the Raspberry-Pi the manual could be downloaded for free.

The Gertduino was a follow up of the Gertboard. There where a lot people who wanted to do more real-time controlling and the discussion Pi or Arduino was a hot topic on a daily basis. Also the Arduino family offered a wide range of ready available plug-on boards which the Raspberry-Pi did not have at that time.
The Gertduino is a Arduino compatible plug-on board which can be placed on top of the Raspberry-Pi and also programmed from the Raspberry-Pi. Besides the standard Arduino configuration it offered more buttons, LEDS and even a second Arduino chip with a real time clock.
Just as with the Gertboard, the final production was done by a retail company, in cooperation with their own manufacturing plant on a royalty basis.

The director and owner of Fen Logic Ltd. was also the chip lead for the BCM2836, the follow up chip for the Raspberry-Pi: the Raspberry-Pi 2.
In fact all the development of products show here where done in the evening hours and weekends, alongside a day time job at Broadcom as Principal Senior ASIC engineer. More information can also be found in the
Gateware section.

The Gertbot product.
Two stacked gertbots controlling 8 motors.

The Gertbot is a plug-on board for the Raspberry Pi which allows controlling various types of motors.
For details see the website:

The Gertbot was completely developed and produced by Fen Logic. The mass-production was done by a Chinese manufacturer.
These are the main steps involved: Here are some related images:
DCC trace
Develop DCC code
GUI screenshot
User debug GUI

Arrival first batch