I thought Millenium was the client but from the website it appears to be the entire suite now. Again this info comes from people who work with the system.

Millenium

Export
Built In. Can dump Marc or CSV files of specific field data
Database Access
Extra. There is a Oracle option with an additional cost with the default being a proprietary database without access. From what I've heard the Oracle tables are not documented overly well. There also appears to be mysql used for some data as well.
API's and Web Services
Extra. Z39 is offered as a product. There used to be an XML server but this appears to have been discontinued. There appears to be more web services in the works though they also appear to be additional products.

Update: There is a xrecord feature built in that allows the pulling of XML data for a specific record, however I’ve never been able to get it to list attached items which reduces the usefulness.