This is a plugin that allows GIMP to read and write RPG Maker 2k/2k3 XYZ files.
The code is adapted from the [WebP Plugin by Nathan Osman] (http://registry.gimp.org/node/25874), though only as a template rather than anything substantial. Nevertheless it retains the GPLv3 as a license.
Make sure to first extract the entire contents of the zip archive first.
Run "install_windows.bat". If you'd like to install for all users, run it as an administrator (right click->Run As Administrator).
Run "install_mac_osx.command" and follow the instructions.
The following commands should do the trick:
make
mkdir -p ~/.gimp-2.8/plug-ins
mv file-xyz.* ~/.gimp-2.8/plug-ins
You may need to configure the makefile and/or source files to properly build it, but the default configuration is most likely fine.