The key thing is being able to open a tab/window in the background, when everything I know of automatically tries to bring any new window to the front. But I do agree with your point: every application seems to be re-inventing its own window/tab/document management instead of using the ones provided by the OS. I used to use Firefox with Tree Style Tabs, but then I found out that having multiple windows full of tabs was good enough, and I can use the OS to just arrange the windows without needing to arrange the tabs therein.