Firebird 2.5.0 RC1
Firebird is a relational database offering many ANSI SQL standard features that runs on Linux, Windows, and a variety of Unix platforms. Firebird 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.
FREE LIKE A BIRD. Anyone can build a custom version of Firebird, as long as the modifications are made available, under the same IDPL licensing, for others to use and build on.
FREE LIKE FREE BEER. No fees for download, registration, licensing or deployment, even you distribute Firebird as part of your commercial software package.