Free Open Source Database Software

What "Free" Means for Database Software

When evaluating free database software, two distinct meanings of "free" apply. "Free as in beer" means the software costs nothing to download and use. "Free as in freedom" means the license grants you the right to study, modify, redistribute, and use the software for any purpose without restriction. The ideal free database software is both: no cost and no licensing restrictions.

The Open Source Initiative (OSI) maintains the formal definition of open source, which requires that the license allow free redistribution, access to source code, derived works, and no discrimination against persons, groups, or fields of endeavor. Databases under OSI-approved licenses (PostgreSQL License, MIT, BSD, Apache 2.0, GPL, LGPL, AGPL) meet both definitions of free. Databases under non-OSI licenses like SSPL or BSL may be free to download and use in many scenarios, but they carry restrictions that prevent certain types of deployment, particularly offering the database as a managed service.

For most application developers, the practical difference matters less than it does for cloud providers and infrastructure companies. But understanding the license protects you from unexpected complications if your deployment model changes, if you are acquired by a company with different legal requirements, or if you want to contribute modifications back to the project.

Free Relational Databases

PostgreSQL (PostgreSQL License)

PostgreSQL is free under the PostgreSQL License, which is functionally equivalent to the MIT and BSD licenses. You can use it for any purpose, modify it, embed it in proprietary products, and distribute it without restriction. There is no dual licensing, no commercial edition with extra features gated behind a paywall (though third-party companies build commercial products on top of PostgreSQL), and no contributor license agreement that could enable a future license change. PostgreSQL is the safest long-term choice from a licensing perspective.

PostgreSQL's feature set is comprehensive: full ACID transactions, advanced SQL compliance, JSONB document storage with indexing, full-text search, extensibility through PostGIS (geospatial), pgvector (AI embeddings), TimescaleDB (time-series), and hundreds of other extensions. It runs on every major operating system and is available as a managed service from every major cloud provider.

MariaDB (GPL)

MariaDB is free under the GNU General Public License. You can use it for any application, modify it, and distribute it. The GPL requires that if you distribute modified versions of MariaDB, your modifications must also be released under the GPL. This does not affect applications that connect to MariaDB over a network, only software that embeds or modifies the MariaDB source code itself. MariaDB is MySQL-compatible, serves as the default MySQL replacement in most Linux distributions, and includes features like Galera Cluster and system-versioned temporal tables that MySQL does not offer.

MySQL Community Edition (GPL)

MySQL Community Edition is free under the GPL with the same terms as MariaDB. Oracle also offers a commercial license for organizations that need to embed MySQL in proprietary products without GPL compliance. For application developers connecting to MySQL as a database server, the GPL Community Edition is free to use without restriction. MySQL is the most widely deployed open source database, with the largest ecosystem of tools, tutorials, hosting providers, and developer familiarity.

SQLite (Public Domain)

SQLite is in the public domain, which means it has no license restrictions whatsoever. You can use it for any purpose, copy it, modify it, and distribute it without any obligation to attribute, open source your code, or pay anyone. SQLite is the most deployed database engine in the world, running on billions of devices as an embedded database in mobile apps, desktop software, browsers, and operating system components. It requires no server, no configuration, and no administration. For embedded and single-user use cases, SQLite is the simplest possible free database.

Free NoSQL and Specialized Databases

Valkey (BSD 3-Clause)

Valkey is the Linux Foundation fork of Redis, created after Redis changed its license to a non-open-source model. Valkey is free under the BSD 3-Clause license with no restrictions. It provides in-memory data structure storage, caching, pub/sub messaging, and streaming with full Redis API compatibility. For caching and in-memory workloads, Valkey is the leading genuinely free option.

Apache Cassandra (Apache 2.0)

Cassandra is free under the Apache 2.0 license. It provides a distributed wide-column store with linear horizontal scaling, tunable consistency, and multi-datacenter replication. The Apache 2.0 license allows unrestricted use, modification, and redistribution including in proprietary products. For large-scale distributed write workloads, Cassandra is the standard free choice.

ClickHouse (Apache 2.0)

ClickHouse is free under the Apache 2.0 license. It provides columnar analytical storage with real-time query performance over billions of rows. ClickHouse is the leading free option for analytics, log analysis, and data warehousing workloads that need interactive query speeds.

Apache CouchDB (Apache 2.0)

CouchDB is free under the Apache 2.0 license. It stores JSON documents, provides a RESTful HTTP API, and supports multi-master replication for offline-first and edge computing applications. CouchDB is a genuinely free alternative to MongoDB for document storage workloads.

Neo4j Community Edition (GPL)

Neo4j Community Edition is free under the GPL for graph database workloads. It supports the Cypher query language for graph traversals and pattern matching. The Enterprise Edition with clustering and advanced features requires a commercial license, but the Community Edition is sufficient for development, small to medium deployments, and learning graph database concepts.

Databases That Are Free but Not Open Source

Several popular databases are free to download and use but carry licenses that the OSI does not recognize as open source. These may be fine for your use case, but you should understand the restrictions before committing to them.

MongoDB uses the Server Side Public License (SSPL), which requires anyone offering MongoDB as a service to release the entire service stack under SSPL. This primarily affects cloud providers, but it means MongoDB is not open source by the OSI definition. Redis (since 2024) uses a dual RSALv2/SSPLv1 license with similar service restrictions. Elasticsearch changed to SSPL in 2021, then later moved to the AGPL (which is OSI-approved). CockroachDB uses the Business Source License, which converts to Apache 2.0 after three years but restricts commercial database-as-a-service offerings during the BSL period.

These databases are all free to use in your own applications. The restrictions apply primarily when you want to offer the database as a hosted service to third parties. If your use case is running the database for your own internal or customer-facing applications (not reselling it as a database service), the practical impact of these license restrictions may be minimal. However, if licensing purity matters to your organization, the genuinely free and open source options listed above are safer long-term choices.

Free Database Tools

The database tools ecosystem is also rich with free options. DBeaver Community Edition (Apache 2.0) is a universal database client supporting dozens of database types. pgAdmin (PostgreSQL License) is the standard PostgreSQL administration tool. Adminer (Apache 2.0/GPL) is a single-file web-based database manager. pgcli and mycli (BSD) are enhanced command-line clients for PostgreSQL and MySQL. pgBackRest (MIT) provides enterprise-grade PostgreSQL backup management. Percona XtraBackup (GPL) handles hot backups for MySQL and MariaDB. Prometheus with postgres_exporter and mysqld_exporter provides free database monitoring.