total web UI to load other web-based subsystems

I have several web based applications with different domains(they are completely separated and run in different machines). I want to have a total web UI container which could load and show all other subsystems menus (like a single page application) and could load their pages inside total UI. In some cases I need to use a service (with its UI) from subsystem A to complete another service from subsystem B. Is there any suggestion or best practice for this? Please take Cross-domain limitation into consideration