Cartesian refers to http://en.wikipedia.org/wiki/Cartesian_coordinate_system. So basicly it uses a number of 'straight' and linear dimensions to indicate a position.
The Ultimaker design is open source. But designs like this are hard to protect by copyright, so even if we wanted to, it would be almost impossible to do so (let alone enforce it).
Personally, I would ask (and its nothing more then asking, your free to not do this) you to open source the designs just like we did, so others can also benefit from it.