Interbase is a RDBMS that is sold by a subsidiary of Inprise. It has since been open-sourced as "Firebird", which can be found at http://firebird.sourceforge.net. If you've heard of it, you know it rocks when compared to SQL Server, Sybase, and Oracle, because it has NO RECORD LOCKING. Instead, from day one it has used a "versioning" system that allows for simultaneous readers and writers with no blocking. It does however, suffer from a lack of "exposure" in the programming community. Free downloads of version 4 are available for Linux and FreeBSD.