CommandBook adds general commands for Bukkit.
You need to have Maven installed (http://maven.apache.org). Once installed, simply run:
mvn clean package install
Maven will automatically download dependencies for you. Note: For that to work, be sure to add Maven to your "PATH".
The issue tracker can be found at http://redmine.sk89q.com/projects/commandbook/issues (we do not use GitHub's issue tracker).
We happily accept contributions. The best way to do this is to fork CommandBook on GitHub, add your changes, and then submit a pull request. We'll look at it, make comments, and merge it into CommandBook if everything works out.
By submitting code, you agree to place to license your code under the irrevocable GNU General Public License v3.