MariaDB is a community-developed fork of the MySQL relational database management system intended to remain free under the GNU GPL. Developed by MariaDB Foundation
License: Open Source
MariaDB is a mature relational database management system with robust SQL support and ACID compliance, making it suitable for traditional applications. In contrast, RethinkDB is designed for real-time web applications, providing built-in support for JSON and horizontal scaling, which makes it ideal for modern, dynamic applications.