How way to load all of my web applications in a web application that i'm working to?

Hi, I'm newbie Web Developer. This is my case:

I have 3 web applications. At the moment I am developing one another to load all of my web apps. You can look at the picture. When I click "button A", so it can load "App A" in red area (I guess i will do it with Ajax), if you have better alternative please tell me.