The best Relational Database alternative to MongoDB is PostgreSQL, which is both free and Open Source. If that doesn't suit you, our users have ranked more than 100 alternatives to MongoDB and many of them are Relational Databases so hopefully you can find a suitable replacement. Other interesting Relational Database alternatives to MongoDB are SQLite, MySQL Community Edition, MariaDB and Microsoft SQL Server.
PostgreSQL is a powerful, open source object-relational database system with over 35 years of active development that has earned it a strong reputation for reliability, feature robustness, and performance.
SQLite is a software library that implements a self-contained, serverless, zero-configuration, transactional SQL database engine. SQLite is the most widely deployed SQL database engine in the world. The source code for SQLite is in the public domain.
MySQL Community Edition is a freely downloadable version of the world's most popular open source database that is supported by an active community of open source developers and enthusiasts.
MariaDB is a backward compatible, drop-in replacement of the MySQL® Database Server. It includes all major open source storage engines.
SQL Server delivers on Microsoft’s Data Platform vision by helping your organization manage your data by enabling you to store data from structured, semi-structured, and unstructured documents within the database.
The Apache Cassandra database is the right choice when you need scalability and high availability without compromising performance.
ArangoDB database is an open-source NoSQL solution with a flexible data model for documents, graphs, and key-values.
Cockroach is a distributed key/value datastore which supports ACID transactional semantics and versioned values as first-class features. The primary design goal is global consistency and survivability, hence the name.
DiceDB is an open-source, fast, reactive, in-memory database optimized for modern hardware. Commonly used as a cache, it offers a familiar interface while enabling real-time data updates through query subscriptions.
is an open-source distributed NoSQL wide-column data store. It is compatible with Apache Cassandra and supports the same protocols (CQL and Thrift) and file formats (SSTable), as well as the Amazon DynamoDB API, and is based on C++20.
YDB is an open source Distributed SQL Database that combines high availability and scalability with strong consistency and ACID transactions.
Firebird is a relational database offering many ANSI SQL-92 features that runs on Linux, Windows, and a variety of Unix platforms. Firebird offers excellent concurrency, high performance, and powerful language support for stored procedures and triggers.
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Postgres now has great support for JSON datatype with indexing, making it a very good document store - plus being the best OS relational DB.