Firebird 
*Platform: Windows, Linux, and macOS. 
*Languages: SQL, C, and C++. 
*Cloud version available: No 
            Firebird was born as a fork of InterBase in 2000, however, it has undergone significant overhaul since then. It's not seen as a direct drop-in replacement for InterBase. Firebird runs on all popular operating systems such as Windows, Linux, and macOS and supports OLTP as well as OLAP applications considering the fact that it has a multi-generational architecture. 

It is completely open source and supports four architectures - Super Classic, Classic, SuperServer, and Embedded. Despite being around for a while,  Firebird doesn't support easy inter-connects with other database software. This has resulted in Firebird not being as popular as some of the other database software mentioned in this list.