ToroDB is a technology designed to fulfill the gap between document oriented and SQL databases. There are two products that use this technology: ToroDB Server and ToroDB Stampede. Both platforms are open source and any feedback, contributions, help and/or patches are very welcome. Please join the torodb-dev mailing list for further discussion.
For more information, please see ToroDB's website
It is a MongoDB-compatible server that supports speaks the MongoDB Wire Protocol (and therefore can be used with the same drivers used to connect to any standard MongoDB server) but stores your data into a reliable and trusted ACID database.
More information about ToroDB Server can be found on its own repository.
ToroDB Stampede is a business analytic solution that replicates your data in real time from a MongoDB replica set into a SQL database, allowing you to use any business intelligence products (like Tableau or Pentaho) to analyze NoSQL data.
As it replicates your MongoDB data, ToroDB Stampede can be used to migrate from MongoDB to SQL databases.