Following the release of Windows Phone, Microsoft underwent a gradual rebranding of its product range throughout 2011 and 2012—the corporation's logos, products, services and websites adopted the principles and concepts of the Metro design language. Microsoft previewed Windows 8, an operating system designed to power both personal computers and tablet computers, in Taipei in June 2011. A developer preview was released on September 13, and was replaced by a consumer preview on February 29, 2012. On May 31, 2012, the preview version was released. On June 18, 2012, Microsoft unveiled the Surface, the first computer in the company's history to have its hardware made by Microsoft. On June 25, Microsoft paid US$1.2 billion to buy the social network Yammer. On July 31, 2012, Microsoft launched the Outlook.com webmail service to compete with Gmail. On September 4, 2012, Microsoft released Windows Server 2012.