Windows 10 build 9841 (fbl release)

Windows 10 build 9841 is the first officially released and the first publicly available Technical Preview build of Windows 10. This build was demonstrated on 30 September 2014 by Microsoft at a closed press conference. It was later released to users who joined the Windows Insider Program on 1 October 2014.

Windows Media Center
If you add Windows Media Center to this build using a purchased Windows 8.1 product key, the system subsequently identifies itself as running "Windows 8.1 Pro with Media Center", along with a warning that the OS has not been activated.

Window thumbnail border color error
If window auto-colorization is enabled, the window thumbnail borders on the taskbar do not change color even after the wallpaper changes. This issue can be remedied by manually changing the window color through the Control Panel or restarting Windows.