If you want to manage an incoming call without interrupting your current activity on the phone, try the new HandyCall from the download link below. It basically transforms the incoming call into a floating popup that hovers on top of anything else you are doing, while still keeping it visible. The popup lets you answer or decline the call, mute the sound, put the caller on speaker, or simply get rid of the popup, and get back to the action. HandyCall also lets you use various visual styles with it - from the orthodox rectangular popup, to the handy floating balloons style. It should work with any Android version, and is completely free for now, so if you are interested in such functionality, you can give it a try and tell us how it went.
source: HandyCall (Play Store)