Plex

Plex was the main visual style for earlier builds of Windows Longhorn. It was featured as the default theme from builds 3683 to 4039. It features an almost all-blue user interface with a prototype sidebar. The theme was removed for build 4042 and replaced with Slate: the development team never intended for Plex to become a finalised theme[source?]; it was intended as a placeholder for the Aero theme which ended up in the final version of Windows Vista.