Boomerang looks interesting in the same way Hyperlapse and Layouts are great apps - a single purpose, focused app that does one thing well but doesn't clutter up the main Instagram app:

...today it’s launching Boomerang on iOS and Android. It’s a dead-simple app where you shoot a one-second burst of five photos that are turned into a silent video that plays forwards and then reverses over and over in a loop.

Source: Instagram’s New Standalone App Boomerang Captures 1-Second Video Loops | TechCrunch

You can download Boomerang for free in the App Store.