SMSD natively supports MySQL and PostgreSQL. However it has also support for libdbi, which provides access to wide range of database engines (eg. SQLite, MS SQL Server, Sybase, Firebird,...). Unfortunately libdbi currently does not work natively on Microsoft Windows, so you can use it only on Unix platforms.
Since version 1.29.92, SMSD can also connect to any ODBC data source, so you should be able to connect to virtually any database engine using this standard.
See also