Firebird is a relational database based on source code that Inprise (now Borland) release as open source. Many features from the ANSI SQL standard are included making Firebird easy to work with if you are experienced with SQL. Firebird database is stable and of production/enterprise quality, and has been widely deployed since 1981. It comes in two models: classic and super server.

The classic version is aimed for single user integration (perhaps embedded into applications) - where the super server version is the stand-alone edition that support multiple clients. Firebird is being very actively maintained by a large team of dedicated developers.