WorldEdit is a voxel and block manipulation library for Minecraft. It is primarily a library but bindings to Bukkit (included) and SPC (external) are available.
You need to have Maven installed (http://maven.apache.org). Once installed, simply run:
mvn clean install
Maven will automatically download dependencies for you. Note: For that to work, be sure to add Maven to your "PATH".
Please submit bug reports and feature requests here: http://redmine.sk89q.com/projects/worldedit/issues
We happily accept contributions. The best way to do this is to fork WorldEdit on GitHub, add your changes, and then submit a pull request. We'll look at it, make comments, and merge it into WorldEdit if everything works out.
Your submissions have to be licensed under the GNU General Public License v3.