MariaDB describes itself as 'An enhanced, drop-in replacement for MySQL'. It is a fork of MySQL led by the original developers of MySQL, created following concerns about the the acquisition of Sun, hence MySQL, by Oracle. The executable names start with 'mysql'. Most Linux distros, including Enterprise grade distros such as Red Hat Enterprise Linux and SUSE Linux Enterprise, now include MariaDB instead of MySQL.
Feature comparison with MySQL and compatibility information can be found at