The Flipboard Explorer, or FLEX, is a component that you can easily drop into any iOS project. When presented, FLEX shows a debugging toolbar that lives in a window above your app. From this toolbar, you can view and modify nearly every piece of state in the application. Unlike many other debugging tools, FLEX works entirely inside your app, so you donʼt need to be connected to LLDB/Xcode or a different remote debugging server. It works well in the simulator and on physical devices.

(via Introducing FLEX — Flipboard Engineering)