Finder

An application was installed on Petronella Osgood's computer by 10 May 2020. Its logo was a square smiley face with roughly one half blue and the other white. (WC: The Zygon Isolation)

Behind the scenes
While the application was not named in WC: The Zygon Isolation, in the real world, this application is called the Finder. This is the default file manager and graphical user interface shell used on all Macintosh operating systems.