It seems there is no equivalent of Python App Engine\'s _ah/admin for the Java implementation of Google App Engine.
Is there a manual way I can browse the datastore?
Open the \war\WEB-INF\appengine-generated\local_db.bin file with a text editor, like Notepad++.
\war\WEB-INF\appengine-generated\local_db.bin
The data is scrambled but at least you can read it and you can copy to extract it.