Microsoft created a secret Windows XP theme back in 2000 that looked a lot like Apple’s Aqua theme. It was used to create the initial theme engine for XP, before its release in 2001.

Say hello to Microsofts Aqua Mac theme
Microsoft created a secret Windows XP theme that made the operating system look more like a Mac. A recent Windows XP source code leak has revealed Microsofts early work on the operating system and some unreleased themes the company created during its early XP development back in 2000.
One is labeled Candy and includes a design that closely resembles Apples Aqua interface that was first introduced at the Macworld Conference & Expo in 2000. Although the theme is incomplete, the Windows XP Start button and various buttons and UI elements are clearly themed to match Apples Aqua.
Microsoft never released its Aqua theme for Windows XP, and we understand it was used in early source code for the OS. Windows developers appear to have used the theme as a placeholder to build the theme engine for Windows XP. The theme itself is described as a Whistler skin with eye candy, and marked as for internal use only. Whistler was the codename for Windows XP.
Windows XP aqua buttons.
Microsoft famously moved to a blue and green Luna theme for the final version of XP, which many dubbed Fisher Price-esque when the OS was originally released in 2001. The theme engine in Windows XP was a major update to the OS, allowing for third-party themes and lots of customizability.
Microsoft was developing Windows XP during an era when there was fierce competition with Apple over desktop operating systems. Later in the 00s, Apple poked fun at Microsoft with banners at its annual developers conference stating Redmond, start your photocopiers. Apple also ran a Get a Mac ad campaign focused on the flaws of Windows, and in particular Windows Vista.
During the 90s and 00s, Windows was heavily influenced by the classic Mac OS and what later became OS X. Apple has also borrowed some Windows features, particularly around windowing, navigation, control panels, and browsing files and folders.
The leak is a rare insight into the early development of an operating system used by millions. Weve reached out to Microsoft to comment on the unreleased Windows XP theme, and well update you accordingly.