FerretDB

FerretDB is an open-source alternative to MongoDB. It works as a proxy that accepts queries in the MongoDB 5.0+ wire protocol, converts them to SQL and stores the data in PostgreSQL with the DocumentDB extension, so existing MongoDB drivers and popular tools can usually talk to it without code changes.

The project was started because MongoDB moved to the SSPL licence, which made it unsuitable for many open-source and early-stage commercial projects. FerretDB targets the common case of developers who want an easy-to-use document database without needing MongoDB's most advanced features, and in many cases it can act as a drop-in replacement. A public roadmap lists known differences and supported commands.

FerretDB is written in Go and released under the Apache-2.0 licence. A Docker quickstart bundles the proxy, PostgreSQL with DocumentDB and the MongoDB Shell for experiments, while separate installation guides cover production setups that do not lose data on shutdown. You run it on your own infrastructure alongside PostgreSQL.