Microsoft may be working on its own tabbed app solution, but if you want to add tabs to any app on your PC now, Stardock's latest app, Groupy, is worth a look. While already available to Stardock's Object Desktop users in beta since November, Groupy is now available for everyone.
Groupy essentially lets you take the tabbed experience from your browser and apply it to any app on your PC. Not only can you use Groupy to consolidate different instances of the same app in one window, but you can bring other apps together in a single window as well.
Using Groupy looks to be pretty simple as well. It operates by simply dragging and dropping apps onto each other to create tabs within a window. This lets you group up programs for specific tasks you may be working on, or simply consolidate all of your open apps into a single window as you see fit. Managing the tabs works just as you've grown used to with a browser, with Groupy allowing you to switch between them with a click. Mouseover previews are also supported so you can preview the contents of a tab before clicking over.