AppEngine : ndb

http://googleappengine.blogspot.com/2011/11/new-datastore-client-library-for-python.html
https://developers.google.com/appengine/docs/python/ndb/ (new datastore)
https://developers.google.com/appengine/docs/python/datastore/ (old datastore)

Some of the benefits of this new library include:

• The StructuredProperty class, which allows entities to have nested structure

• Integrated two-level caching, using both memcache and a per-request in-process cache

• High-level asynchronous API using Python generators as coroutines (PEP 342)

• New, cleaner implementations of Key, Model, Property and Query classes