If you are a Windows Phone app developer, you can check out the features of a more recent version of Windows 10 for phone via the emulator included in the latest Visual Studio tools release. The build number for this version is 10069, while the current version for Windows Insider members is 10051.
WinBeta went over some of the new features it found while using the emulator in a video. They include a Start screen which have its Live tiles closer together compared to previous versions. The build also includes some new built-in apps like the revamped beta version of the Windows Phone Store, and a new Get Started app that offers information for new Windows Phone users on the basics of the new OS. Finally, there are some new customization options for the Start Screen, including some new colors and more.
Keep in mind that this emulator is designed to be used just by app developers. If you are a regular Windows Phone consumer, we highly recommend that you don't download the Visual Studio tools just to check out the features in this build, as it will almost certainly be full of bugs and performance issues. Microsoft is expected to release a new Windows 10 for phone build to Windows Insider members sometime early next week, after missing a previously announced deadline for the end of April. The new build should also have support for the new universal Office apps for phones.