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Riak - A Decentralized Database
Highly Scalable Data Stores
ZODB vs. pysqlite with SQLObject
two good options for an embedded, transactional database that can be conveniently used in a non-free Python…
PostgreSQL
torodb/stampede
The ToroDB solution to provide better analytics on top of MongoDB and make it easier to migrate from MongoDB to SQL
Open source olap on Wikipedia
Good number of links to various FOSS implementations.