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
Object-Relational Main-Memory Embedded Database system tightly integrated with C++ language. Use OS virtual mapping mechanism to access data. Provides subset of SQL language with OO extensions. Support of transactions, fault tolerance, replication.