For two periods last year, those using preview builds of Windows 10 could access to a feature called Sets: a tabbed interface that was eventually to allow tabs to be put in the titlebar of just about any window. These tabs would allow both multiple copies of the same application to be combined—a tabbed Explorer or Command Prompt, say—and multiple disparate windows to be grouped—combining, say, a browser window containing research with the Word window. However, both times the feature was enabled only for a few weeks, so Microsoft could gather data, before disabling it. Sets aren't in the Windows 10 May 2019 update.
The Shell-provided tab experience is no more, but adding tabs is high on our to do list.
— Rich Turner (@richturn_ms) April 20, 2019
It seems now that Sets are unlikely to ever materialize. Rich Turner, who oversees Microsoft's revamping of the Windows command-line infrastructure and the Windows Subsystem for Linux tweeted that the interface "is no more." Having everything tabbed everywhere isn't going to happen. Adding tabs specifically for command-line windows is, however, "high on [Microsoft's] to do list."
(Score: 2) by shortscreen on Thursday April 25 2019, @03:36AM
The old (real) Opera used MDI. Tabs were just another way to switch between child windows, rather than using a drop-down list or having to minimize one to reveal another. But the tabs could still be tiled or cascaded just like Windows 3.1 Program Manager. It also allowed multiple (parent) windows, but unfortunately they all ran under the same process.