Firebird is a relational database offering many ANSI SQL standard features that runs on Linux, Windows, and a variety of Unix platforms.
It offers excellent concurrency, high performance, and powerful language support for stored procedures and triggers. It has been used in production systems, under a variety of names, since 1981.
The Firebird Project is a commercially independent project of C and C++ programmers, technical advisors and supporters developing and enhancing a multi-platform relational database management system based on the source code released by Inprise Corp (now known as Borland Software Corp) on 25 July, 2000. The Firebird software is free. That means anyone can build a custom version of it, as long as that person or organisation is willing to provide the modifications, under the same IDPL licensing, for others to use.
Firebird is also completely free of any registration, licensing or deployment fees. It may be deployed freely for use with any third-party software, whether commercial or not.