This article could be expanded on and use more details, and needs them as much as XP-tan needs more RAM!
Windows 10 is the current release of the Windows operating system, and the successor to Windows 8.1. It was released by Microsoft for personal computers, including home and business desktops, laptops, tablets, and home theater PCs, as well as Mobile devices, such as ARM Tablets and Phones. Windows 10 marks a shift in Microsoft's strategy by allowing iOS and Win32 applications to be compiled as WinRT applications, and by changing the Windows distribution model to what has been dubbed as "Windows as a service", with free updates that bring new features and functionality, as opposed to previous operating systems that only received major features and functionality through either service packs or paid upgrades to a newer version. It also is the first Windows to be widely available for public testing early on in the development with the ability to give feedback, helping shape Windows to best suit it's customers' needs.
Windows 10 implements an adjustable "hybrid" menu system that combines the best of both the Start Menu and Start Screen, and uses "Continuum" to seamlessly select the best layout and method of interaction based on the device and it's current state (I.E laptop, tablet, 2-in-1 tablet-mode/pc-mode). It also introduces the successor to Internet Explorer, named "Microsoft Edge", which is a more lightweight browser has been stripped of legacy components used for compatibility with outdated webpages built for older browsers.
Madobe Touko (窓辺 とうこ) is an official mascot from Microsoft. What is known about her:
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She is voiced by Ai Nonaka (of Puella Magi fame as Kyouko Sakura). She did not originally have a confirmed name when she made her public debut, and a contest was held on June 19, 2015 to determine what it would be, with participants eligible to win a number of gifts, including 5 grand prizes autographed by Ai Nonaka herself. Her name was revealed to be Madobe Touko in July 2015.
Other Windows 10-tan designs have been drawn by artists on Pixiv.
Official contest page of Windows 10-tan (Japanese)