FerretDB
A truly Open Source MongoDB alternative
... queries to SQL, and uses PostgreSQL as a database engine. This will be compatible with MongoDB drivers, and should work as a drop-in replacement to MongoDB in many cases. Our vision is to enable the open source community and developers to reap the benefits of easy-to-use document databases, while staying away from vendor lock-in, and fauxpen licenses. We are open source advocates at heart, and we release FerretDB with an open source license recognized by the Open Source Initiative.