http://www.techradar.com/news/you-could-soon-try-out-new-features-of-windows-10-apps-without-being-a-windows-insider

It appears that Microsoft may be planning to allow Windows 10 users to test preview versions of the operating system’s core apps without having to sign up to be a Windows Insider.

In other words, folks running the normal (retail) version of Windows 10 will be able to play around with standalone preview versions of these apps, and test out their new features, without having to sign up and install the preview build of Windows 10.