Tabs come to every window in Windows 10 “Sets”
The basics of window management in Windows haven't really changed a whole lot since the days of Windows 3. You can maximize windows to make them take up a whole monitor or you can have them free-floating and arbitrarily sized—that's about it. macOS gives maximized windows a slight twist with its full-screen view, and Windows 7 introduced Aero Snap, a way to get two windows side by side, each occupying exactly half the screen (later extended to divide the screen into quadrants, for four windows at a time). While these are both compelling features, the basics still haven't really changed for decades.
But one kind of application has long stood out as an exception: the browser. Browsers add a second dimension to window management through their use of tabs. While browsers probably weren't the first, and certainly aren't the only, apps to have tabs, they're the ones that have done so most successfully. With tabs, we can have multiple pages—multiple discrete activities—all within the same window. We can combine tabs with other window management to, for example, put a bunch of related tabs in a particular window, grouping them up and handling them as a unit.
In a feature announced today, Microsoft is going to bring that same kind of two-level grouping and management to every window and every application. Tabs won't just be for browsers; they'll be for Notepad, or Word, or Visual Studio, or Explorer, or Minecraft. The feature is currently called "Sets," and it'll be coming soon to the Windows Insider Program.