The source code directory structure for JPA Objects is as follows:

trunk/
  main/               # main release for JPA, including Maven site
    applib/             # the JPA application library
    metamodel/          # adds JPA semantics into the NO metamodel
    runtime/            # JPA runtime support (uses Hibernate)
    tools/              # DBA support for schema and fixture management (uses Hibernate)
    documentation/      # this documentation
  support/            # support release for JPA
    release/              # defines dependencies for projects using the 'fixtures' module
    archetype/            # archetype - released after the main release
  testapp/            # application for testing - not released
tags/
  main                # tags for trunk/main
  support             # tags for trunk/support

As is usual, to ensure that tags go into the correct location when releasing, the mvn-release-plugin plugin has been configured (using <tagBase>) to override its default location.

You can checkout the entire trunk using Subversion:

svn co https://jpaobjects.svn.sourceforge.net/svnroot/jpaobjects/trunk ~/jpaobjects/trunk