Inter Base
"Borland InterBase 6.5 is a high-performance, cross-platform, SQL standards-compliant RelationalDatabase that combines ease of use, low maintenance costs, and enterprise power. Certified by Borland, InterBase 6.5 provides the flexibility required for Internet, mobile, and EmbeddedDatabase applications. InterBase supports all popular DesktopClients and ApplicationBuilderFrameworks."
Interbase 6.01 has been released as open source
http://www.borland.com/devsupport/interbase/opensource/
and is being developed as FireBird