Each CMS needs a driver, and each application needs a driver. An application with a driver can be run from any CMS with a driver.
I have just completed the CMS Bridge driver for PostNuke. On the Demo and Dev site, I have a bridge to phpBB2.
The bridge to PostNuke is working, but not quite ready for release. I need to update documentation and tarfiles first.
CMS-Bridge is licensed under gnu LGPL