Compatible with iOS 8
Also available, WhitelistSwitcher9 (iOS 9)
"WhitelistSwitcher" cleans up a messy, cluttered App Switcher.
You pick the applications you care about, hit enable WhitelistSwitcher, and even if you use other applications once or twice, only the apps you care about show up in the switcher.
Compatible with the latest iOS 8, tested on an iPhone 6 Plus 8.1.2.
Configure options from Settings.