ManifoldCF runs on top of a MySQL database.
Support for MariaDB (https://mariadb.org) should be easy to implement since MariaDB is binary compatible to MySQL.
DBInterfaceMySQL already works on top of a MariaDB. But using the MariaDB Java Client is not possible since the MariaDB driver has a different class name: org.mariadb.jdbc.Driver.
A new database implementation DBInterfaceMariaDB extending the existing DBInterfaceMySQL should solve this. Minor adjustments to DBInterfaceMySQL are necessary, since the JDBC driver class is currently passed to the super constructor which makes it hard to replace it. (see provided patch)
Due to license issues (LGPL), the MariaDB JDBC driver cannot be shipped with ManifoldCF.