Final Config implements the preference dialogue (typically found under Edit->Preferences) as a separate application that can be used by another application (called the client application or client) through DBus. The available preferences and how they are to be presented to the user is described in an XML file (the desc file), which can be stored in a place convenient to the client. The client does not need to bother with the desc file; it just needs to pass along the file location when invoking the FinalConfig service.
MCM is a set of tools that ease the management of multiple servers. It's aimed at network or system administrators who need to connect to different servers by different means every day. It can be used via an ncurses interface without requiring an X server, and via a GNOME-based GUI.