We're always looking for more contributors! ghost2 welcomes Java developers of all types and all experience levels. To start programming with us, read the contributor's guide on the wiki for an extensive guide on cloning ghost2 and working with the command classes. If you have a decent amount of experience with Java, feel free to submit pull requests for general code improvements in other parts of the project as well; be aware that full documentation is currently a work-in-progress, though.
ghost2 is licensed under the GPL, so you are entirely permitted to redistribute your own version or reuse part of the code as long as you follow the license terms.
As a final note: whether you're a developer or not, if you find any issues that haven't been documented yet, please by all means submit them to our issue list.