MariaDB

MariaDB is a community-developed branch of the MySQL database, the impetus being the community maintenance of its free status under the GNU GPL, as opposed to any uncertainty of MySQL license status under its current ownership by Oracle.
The intent also being to maintain high fidelity with MySQL, ensuring a "drop-in" replacement capability with library binary equivalency and exacting matching with MySQL APIs and commands. It includes the XtraDB storage engine as a replacement for InnoDB,[1] as well as a new storage engine, Aria, that intends to be both a transactional and non-transactional engine perhaps even included in future versions of MySQL.[2]
Its lead developer is Monty Widenius, the founder of MySQL and Monty Program AB.