Quickly switch back to in-progress call or navigation? One of my favorite iOS features is that, when you have a call or turn-by-turn navigation in progress and switch apps, you can easily return just by tapping the status bar. 

In android, I've noticed a number of apps that can show floating widgets over other apps - Facebook messenger's floating "chat heads" and CyanogenMod's floating calculator widget are good examples.

Is there any way to make similar floating icons appear when on a call or when navigating in the background, that when tapped will quickly return to the relevant app?
In Android 4.4 on Samsung Note 4, while you are using an app, phone calls will pop up as a small moveable window on top of that current running android app. You can maximise/minimize that moveable window. This might be a better solution to multitasking while having a phone call on the same device. I am not sure cyanogenmod have the similar features, though.

However, stock Android 4.4, have a pull down notifications window. Applications such as Google Maps Directions and Waze, will put a notification icon in the notifications status bar while you are navigating, so pulling down the notifications window will allow you easy access to switch back to the navigation application. As the screenshots shows the notification window have resume navigation bar at constant place in the middle of the screen, on top of other notifications.