Middleware is software that runs in the middle tier of a Three Tier? system of User Interface (Front End or Client), Application Server, and Database Server? (Backend).

Whereas web client software has a limited number of languages (generally HTML and Javascript, sometimes Java applets or Active-X Controls) and the Database is generally accessed via standard SQL, middleware languages and development frameworks used on the application server are diverse and many - notably Perl, PHP, ASP and .NET (Visual Basic, VBScript, C#), JSP, Java, C++, Tcl, Python, etc.

Be aware that your choice of a CMS Frame Work will be a commitment to a distinct software developer community. If you have developers in your organization already, make sure they buy in to your CMS selection.