MapReduce Open Source
App Engine MapReduce is an open source library that is built on top of App Engine services, including Datastore and Task Queues. You must include the library with your application, it provides:
•A programming model for large-scale distributed data processing
•Automatic parallelization and distribution within your existing codebase
•Access to Google-scale data storage
•I/O scheduling
•Fault-tolerance, handling of exceptions
•User tunable settings to optimize for speed/cost
•Tools for monitoring status