I downloaded a scanner app and found it in my multi window tray. How did that happen?

[AC Question]

I cannot find a way to add apps to my S3 multi-window but I downloaded a scanner app and somehow it was added to my m-w tray. How did that happen?

 

[AlphaTango414]

All compatible apps are listed when you long press your recent key. You can not "add or delete" apps from this. Not all apps are developed to be used with that feature.