I've started a native C-language port of the interface to the CrazyRadio and CrazyFlie. Why? Because it's fun, and because I wanted to really understand how the low level stuff worked. I could have used the libcflie code (https://github.com/fairlight1337/libcflie) by Jan Winkler but I don't like C++ (understatement) and besides, I really wanted to learn.
The code is released GPL3 and it's here: https://github.com/gherlein/libcf2
This code is NOT yet working. I think I have it started sending packets to the cf2, but my reads of the ACK always only have one byte (status byte). I don't think this is right. If I use the python client and use the tool off the "View|Toolbox|Crtp Sniffer" and sending the same messages I don't get the same reply. So my code is still broken.
Assistance is welcome. Please just submit pull requests.