Firebird RDBMS offers ANSI SQL features & runs on Linux, Windows & several Unix platforms. Features excellent concurrency & performance & powerful stored procedure & trigger language.
More information and downloads at https://firebirdsql.org/, issue tracker is https://github.com/FirebirdSQL/firebird/issues
A C++ database connectivity class library supporting different database management systems under a simple interface. The API is hiding implementation details from developers, so class usage is same for each database management system.
602SQL Open Server is a relational database management system for MS Windows and Linux based on ANSI SQL. The system provides ODBC, PHP and SDBC (for OpenOffice integration) connectivity, along with a graphical development environment and SQL debugger.