If you are a new developer to Turbine or even an existing developer, these are areas where you can take ownership and help complete. Please do not ask us how you can help, but rather specific questions about how you think that these items should be implemented. It is up to you to take initiative and provide solutions to the missing functionality described below. ;-)
It is always possible to take ownership of any portion of the project. The way to do this is to post a message to the turbine-dev mailing list. Just explain what you are wanting to work on or any ideas that you might have on the subject.
Documentation is *always* appreciated in any form. The documentation for Turbine exists in basically four forms.
Testing is another area in which help is always needed. This could consist of simply reporting problems that you run into using Turbine. It could also consist of submitting code to perform unit tests. Turbine uses JUnit and Cactus for testing. You can find examples in the src/test directory of the source distribution.
If you do discover a defect in the Turbine product, please create a defect issue in the issue tracking system clearly discribing the problem. If you can take the time to track down the source of the problem, it would certainly help speed the process of getting it corrected. Of course, actually fixing the problem and attaching a patch to the issue would be greatly appreciated.
You can also contribute to the project by enhancing existing functionality and/or adding new functionality. There is a current list of requested features on the Turbine Wiki. Everyone is encouraged to take part in the discussion, design, and implementation.