Source: Microsoft
With Insider Preview Build 17618 Microsoft implemented the sets which were already seen a year ago in a preview build but Microsoft removed i t quickly without any explanation. But here are finally the sets, which implement Windows 10 UWP Apps in an Edge like Browser Interface with tabs. Things like the calendar or the mail app are now presented in tabs you can easily swich between. But also normal web browsing or Office and Office Online are shown in the same Edge window. Microsoft is already working on the implementation of system32 apps/programs such as the Explorer or the Command Prompt which are already implemented in the Edge environment but still need a polish.
Source: Microsoft