ComputerAssociates announced in a May 2004 that Ingress was to be made available under the CA OpenSource license (which they catchily titled the CA Trusted Open Source License).
News.com covered it : http://news.com.com/CA+open-sources+Ingres+database/2100-7344_3-5219373.html?tag=nefd.top
The source code and binary packages for Windows, Linix/x86 and Solaris/SPARC have since been made available at the project home page.
It is my understanding that CA wished to make their database the storage engine of choice for Zope, Plone and JBoss. I also believe that Ingres is the data engine behind the CA network management suite of applications.
I have not personally used Ingres as a database for my own applications so I can not comment on how suitable it would be as a replacement for Postgresql, MySql, Firebird or the commercial rdbms.