Would you like some Mongo with your Postgres?

Speaking of PostgreSQL, ToroDB is a JSON database that runs on top of Postgres.

JSON documents are stored relationally, not as a blob/jsonb. This leads to significant storage and I/O savings. It speaks natively the MongoDB protocol, meaning that it can be used with any mongo-compatible client.

MongoDB client compatibility. Smart. Still early days, though:

ToroDB follows a RERO (Release Early, Release Often) policy. Current version is considered a "developer preview" and hence is not suitable for production use. However, any feedback, contributions, help and/or patches are very welcome.