XDR is actually a part of the Sun RPC mechanism which seems to be implemented on nearly all Unix systems.
Some documentation is included in the distribution.
These operators work on generic netCDF files and perform rote tasks like renaming, concatentation, hyperslabbing, averaging, interpolation, and differencing. The documentation is nearly complete. All known bugs in version 0.9 have been fixed. The manual is nearly complete, and describes all operators. I can get their example program to run fine, but it isn't XDR oriented.