WhatsOpen is a free utility for Mac that enhances system visibility by displaying all open files and folders. This tool allows users to gain insights into what applications and processes are currently accessing specific files. It provides a straightforward interface, making it easy to navigate through the system's open resources and understand their usage.

Key features of WhatsOpen include the ability to quickly identify which applications are using particular files, as well as the option to close those applications directly from the interface. This functionality is especially useful for users looking to manage their system’s performance more effectively. Furthermore, WhatsOpen is lightweight and does not require extensive system resources, making it an ideal choice for those seeking a simple yet powerful tool.