JabRef needs to connect to a MySQL database. See Shared SQL Database for more information.
Use MariaDB Connector
Use MySQL Connector
Other alternatives are listed at https://stackoverflow.com/a/31312280/873282.
Chosen option: "Use MariaDB Connector", because comes out best (see below).
The MariaDB Connector is a LGPL-licensed JDBC driver to connect to MySQL and MariaDB.
Good, because can be used as drop-in replacement for MySQL connectopr
The MySQL Connector is distributed by Oracle and licensed under GPL-2. Source: https://downloads.mysql.com/docs/licenses/connector-j-8.0-gpl-en.pdf. Oracle added the Universal FOSS Exception, Version 1.0 to it, which seems to limit the effects of GPL. More information on the FOSS Exception are available at https://www.mysql.com/de/about/legal/licensing/foss-exception/.
Good, because it stems from the same development team than MySQL
Bad, because the "Universal FOSS Exception" makes licensing more complicated.