When you want to hang a picture on the wall or perfectly level a piece of furniture, you don't need any fancy leveler that's just plain uncomfortable to use. All you actually need is your iPhone. No additional apps.
Did you know that the Compass app that comes bundled in right in your iOS has a built in leveler? Just swipe left in the app and your iPhone becomes an instant perfect leveler that you can actually hold in your (one) hand. Compass might ask you first to calibrate the phone by rotating it so that the ball travels on the circle on the screen. It's annoying, but necessary.
So next time you want to align that family photo on the wall, don't yell for help from the person behind you. They don't have the perfect leveler that you have right in your pocket.