aetycoon provides a library of useful App Engine datastore property classes. The property classes included here cover use cases that are too specialized to be included in the SDK, or simply weren't included, but are nevertheless generally useful. They include: - DerivedProperty, which allows you to automatically generate values - LowerCaseProperty, which stores the lower-cased value of another property - LengthProperty, which stores the length of another property With aetycoon, you'll have all the properties you're ever likely to need.