Windows 10 Mobile's 'hidden' landscape UI
(All About Windows Phone)

Now, don`t get too excited, I haven`t found a hack to get the Start screen to work in landscape mode (though this was planned at one point by Microsoft) - but I`ve made some pleasing discoveries with some built-in and third party applications. Which is as expected, really - if Windows 10 Mobile can expand and re-arrange its screen output for a large Continuum display then we should expect some sense of that when our phones are rotated and their (horizontal) screen size suddenly doubles.