MariaDB is based on the MySQL server 5.1 code base and offers an interesting alternative to MySQL in light of the uncertaintity about the long term licensing policy for MySQL.
Both databases are released under the GPL v2 license.
See the MariaDB developers' comparison for more information about the compatibility of MariaDB and MySQL.
That MariaDB is a robust and long term alternative to MySQL can be seen, for example, in that it is now used for the Wikipedia sites instead of MySQL.
See the MariaDB developer's licence FAQ for more information about the licensing issues around the use of MariaDB.
We have not tested JobScheduler with MariaDB server but have tested it with the MariaDB JDBC connector (version 1.1.3 and newer) and as of JobScheduler version 1.5.x are including the connector in the JobScheduler installation file.
The MariaDB JDBC connector is released under the LGPL license which allows us to bundle it with JobScheduler.