An open-source DBMS platform descended from Interbase.
Firebird is a descended from Interbase, a DBMS platform widely used during the 1980s and 1990s, particularly in SME environments. Released as an open-source project, it has evolved substantially and has a substantial user base. It is a stronger transaction processing system than MySQL, but not so tuned to large transaction volumes, so it is more suited to a conventional business application than a high-volume web site.
An oracle emulation layer, Fyracle, was produced to use with Compiere, an open-source ERP system. Compiere was originally developed on Oracle, and has substantial dependency on Oracle-specific features. Fyracle was developed to remove the Oracle dependency of Compiere, so it could be deployed as a 100% open-source solution with no licensing constraints from Oracle.