I read several threads and did a google search.
I found some C++ implementation of the Digi’s API but nothing in standard C - I mean to use with microcontrollers.
It’s not hard to write my own library (though VERY long due to the large set of options and variations) but I wonder if Digi provides or recommends an existing implementation.
To the best of my knowledge, http://code.google.com/p/libxbee/ is your only hope. I guess Digi don’t recommend any lib file to use with microcontrollers.