Back to RPi Expansion Boards.
The Gertboard is one of the expansion boards, sold for some time in a kit form. It was nicknamed after Gert van Loo, its developer and one of the principal Hardware Engineers for Raspberry Pi, and was announced on 17th December 2011: 
Gertboard Availability Announcement includes links to assembly and user manuals.
Additional Details can be found on the Raspberry Pi Forum here.
As of 2012-11-01, it is not possible to order Gertboard. In Element14 words: "Sorry to disappoint, we have decided to remove the Gertboard from sale. Don’t worry we are planning on producing a fully assembled board but this will not be available for another few weeks." 
Gertboard test suite has been released in Python. These are written to be functionally identical to the original C programs, but have been rewritten from scratch. There are versions for WiringPi for Python and RPi.GPIO.