Using the bulkloader.py utility you can download all data from your application's Datastore.
It is not obvious how the data is stored, however. From the looks of it, you get a SQLite file with all data in binary format in a single table:
sqlite> .tables
bulkloader_database_signature result
sqlite> .schema result
CREATE TABLE result (
id BLOB primary key,
value BLOB not null,
sort_key BLOB);
Are there any tools to work with this data?