CALI is a center for projects to make legal materials freely available.
A recent example would be the Federal Rules of Civil Procedure, Federal Rules of Criminal Procedure and the Federal Rules of Evidence in free ebook form.
All three of which could be mapped into current case law streams, or other topic map type projects.
If you are interested in law and topic map type projects, CALI would be a good starting point for inquiries into what is needed the most.
PS: If you can, please join CALI to support their work.