command the NXT using C

[pepijndevos]

Is there anything? I know of libs for C# and Python, but not C. Do you just talk to the phantom driver? That's not available for Linux, right?

[spillerrec]

I have been using Ander's (something) C++ library: http://www.norgesgade14.dk/bluetoothlibrary.php That's is C++ though. However someone ported the old version to Linux, which you can find there too.
You can download the required files and documentation to work with the fantom driver from Lego's Mindstorms download page, however it is Windows and Mac only. Secondly, that is C++ too.

As far as I understand, most libraries on Linux directly interacts with the NXT using USB/BT commands, thus implements the driver themselves.

I would love to have something that worked on Linux, OS X and Windows, but so far I didn't find anything that I liked. (I want to add file upload/download directly in RICcreator, but it seems like it might become a windows only feature...)
I found another library which had dropped support for Linux (and thus only the older version could be used in both), but I didn't manage to get that running (and can't remember the name). I had to fix compile errors in Ander's library too though... That was again, C++.