APIs have been made available which allow clients to extend Domino Designer. The Domino Designer Extensibility API Javadoc documents all of the public APIs that are available to clients.
In this webcast, the Consultant In Your Pocket series discusses what's new in IBM Domino Designer 9.0
These videos are from a TLCCGBS webinar in November, 2011. The topic is using the new Relational controls in the Extension Library.