The best open source alternative to Oracle Database is SQLite. If that doesn't suit you, our users have ranked more than 50 alternatives to Oracle Database and many of them is open source so hopefully you can find a suitable replacement. Other interesting open source alternatives to Oracle Database are PostgreSQL, MySQL Community Edition, Sequel Pro and Ubicloud.
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.
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.
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.
Sequel Pro is a fast, easy-to-use Mac database management application for working with MySQL databases.
Open, free, and portable cloud. Elastic compute, block storage (non replicated), and virtual networking services in public alpha.
The Apache Cassandra database is the right choice when you need scalability and high availability without compromising performance.
A full-stack, syncing database that runs on both server and client. Pluggable storage (indexeddb, sqlite, durable objects), syncs over websockets, and works with your favorite framework (React, Solid, Vue, Svelte).
Filesystem-backed document DBMS in Rust where every record is a Git-versionable JSON file with automatic cryptographic integrity for compliance-critical systems.
FerretDB (formerly MangoDB) is an open-source proxy, which converts MongoDB wire protocol queries to SQL, and uses PostgreSQL as a database engine.
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.
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First of all its most comparable to Oracle compared to the other solutions in this list. You are not limited to JSON, don't neet to jump to NoSQL. This doesn't mean that PostgreSQL is a FOSS alternative to Oracle. Programming in the database is quite different.