Tab trees

I may be missing something obvious, but I haven't found a good way to manage having many files open related to the same project. The tab bar gets cluttered very quickly and the side bar takes up too much space. Having more than one window isn't ideal either.

It'd be nice if you could group tabs with another, user-named, tab. These would be stacked such that the tab bar is two (or more) rows high, forming a sort of tree. You'd be able to build up a view of the part of the project you're working on and organize components as they relate to what you're doing (instead of the side bar directory view, since the directory structure may not mimic your current mental hierarchy)

,__________________.___________________.__________________,

|        UI        |      Network      |      Engine      |

-------------------'                   '------------------'

|    tcp.c   |    quux.h   |    baz.c    |    foo.c       |