Is there a way to add more apps into the multi window?

[dfman]

One some apps are available in the multi window sidebar (I already pressed the edit button, the app is not inside there). Is there a way to add more apps that are not shown inside multi window sidebar and edit button?

I am using Samsung S4

 

[bsweetness]

With the stock software, you can only add the apps that the edit button will you allow to add. Apps must have multi-window support in order to function with the stock software, and most apps don't have that support built in. There are ways to add additional apps if you're rooted or running a custom ROM, but I'm not familiar enough with them to offer much in the way of advice.