MacOS Sierra Features: Tabs
Even though Tabs was one of the important features of OS X, not all apps were using them. However, macOS is all about Tabs.
With macOS, all Apple apps including Safari, Finder, Pages, Keynote, Numbers, etc support the Tabs naturally. However, most importantly, all apps will be using Tabs and there is no need for developers to do anything. The operating system will integrate tabs to the apps without asking developers to change the codes.