The other available German Whist software implementations (notably the one by MeggieSoft) are shareware. First of all, this means that you will eventually have to pay for it. Secondly, it means that it is not open source, so you cannot learn from the source code and cannot modify and release your own variation. PyGermanWhist is also written in Python, a good language that is relatively easy to learn.
To use the program:
Alternatively, you can use the uncompiled set of scripts:
Download PyGermanWhist*
*If you choose to use the scripts, you will also need the following prerequisites:
http://www.python.org/download/releases/
http://www.wxpython.org/download.php
If you don't know how to play German Whist or have never heard of it, here is a link to the standard rules (it is a lot like Spades): http://www.pagat.com/whist/german_whist.html
Any comments or questions?
Have fun!