WinRunner is a functionality and regression testing tool developed by Mercury Interactive (now HP) for testing graphical user interface (GUI) applications. It uses object-oriented technology to recognize each control/field in an application as an object and stores objects and their properties in a GUI map file. WinRunner allows recording and playing back tests, inserting checkpoints, synchronizations, and more. It also supports features like data-driven testing, recovery scenarios, debugging tools, and batch testing of multiple scripts.