The incoming call screen got a big overhaul in Android 4.0 last year, but it's still not perfect. An incoming call pulls you away from what you might be doing with your phone. Writing an email? Not anymore you're not. Reading a webpage? You can reload that after the phone call. Small Call notifies you of incoming calls in an unobtrusive way while still preserving functionality.
When your phone rings, Small Call will pop up a floating bar at the bottom of your screen. It has answer and ignore buttons on the sides, and a text button in the middle.