Switchr - App Switcher is an app that lets you alternate between the different apps you have running in the background on your Android. In the settings, you can find four different view modes that let you customize how you want to switch between the apps.
Switchr - App Switcher is a great app, but unfortunately, it doesn't work on Android 5.0 or higher. This means you can only use it on devices with Android 4.3 or lower. Otherwise, it just doesn't work, since no apps appear to be running in the background.