It looks like an unreleased build of Windows 10 has leaked onto the web. Build 9888, which was covered exclusively here at WinBeta recently, has started popping up on a number of different file-sharing websites. Build 9888 is probably most known for being one of the first builds with a new NT kernel version of 10.0.
As per all leaks, WinBeta will not be linking directly to the download, and we also advise you do not download unreleased software. Build 9888 is a build intended for partners, not Windows Insiders. You have been warned. We've already covered this build, so if you wish to take a look at what's new without downloading and installing build 9888, watch the embedded video below.
WinBeta is also yet to confirm the legitimacy of this leak, so stay cautious. Build 9888 includes additional window animations, changes to the Settings app and the beginnings of unified context menus.