Download
The nearest-neighbor lookup example program is free software, distributed under the GNU General Public License. The program contains part of my Misc, Math, and Geometry libraries, but is self-contained and comes with a makefile that should build it under Linux. The program is console-based, and should (at least in theory) compile under all kinds of Unix-like operating systems, Mac OS X, and even Windows (though you will need a real C++ compiler, and your mileage may vary).
The tarball available for download below will expand into a NearestNeighbors directory in the current directory. All downloadable files are tagged with their SHA1 checksums to protect against corruption and tampering.
News: The tarball was updated 04/08/2006 to include the newest version of the kd-tree class.