Lenka (US$2.99) is a simple app to help you create dramatic black and white images. The app was developed by famed photographer Kevin Abosch and it's starkly simple. To begin with, you frame your photo, which is visible in black and white in real time on your iPhone. There are only a couple of options: regular or high contrast. You can change the format from rectangular to square, and then you can start firing away. The only available editing tools allow rotation and cropping.
That may seem like a pretty sparse feature set, but the idea here is to get the picture right, then take it. The author considers the use of filters a potential distraction. Still, there's nothing that keeps you from importing your photo into another editing app on your own.
The photos taken with Lenka look very good. A great deal of thought has been applied to matching to software to the characteristics of the iPhone camera hardware. (The developers recommend an iPhone 5, 5c or 5s, but the app will work on older iPhones.) Lenka will autofocus, or you can tap the screen to selectively focus on a specific point.