Wikipedia defines composite applications as "... a perspective of software engineering that defines an application built by combining multiple services. A composite application consists of functionality drawn from several different sources ..."
What the composite "container" might be could, vary from a portal approach, to a richer smart client perhaps built in WinForms or perhaps Java client technology.
What many folks don't know is that Office 2007 makes a great platform (yes I said PLATFORM!) that provides rich services for composition of presentation, logic and data.
There is now a book available about composite applications and how they can be developed using the 2007 Microsoft Office System. This is a good reference that provides an overview of the technologies available in the 2007 Microsoft Office System, and gives several examples from various industries of how to build Office Business Applications.
Check it out at http://msdn2.Microsoft.com/en-us/library/bb220803.aspx