MariaDB 5.5 is a stable (GA) release of MariaDB. It is MariaDB 5.3 + MySQL 5.5.
See "What is MariaDB 5.5" for an overview of what is in MariaDB 5.5.
MariaDB Connector/J is used to connect applications developed in Java to MariaDB and MySQL databases. The client library is LGPL licensed.
See this article for more information
MariaDB Connector/C is used to connect applications developed in C/C++ to MariaDB and MySQL databases.The library is LGPL licensed.
See the MariaDB Connector/C section of the MariaDB Knowledge Base for more information.
MariaDB Connector/ODBC is an LGPL licensed, standardized database driver for Windows platforms. It supports ODBC Standard 3.5 and can be used as a drop-in replacement for MySQL Connector/ODBC.
The MariaDB Connector/ODBC section of the MariaDB Knowledge Base contains more information.