Integrate external files into the trees

Often there are external files or web links you'd like to associate. If that ability were incorporated (you could color code them) it would make concept and project management much, much easier. And if the external file were a program (like Project, Powerpoint, etc.) you could link for execution, with the file name passed as a parameter. You'd have all your linking done, and people wouldn't have to jump in and out of your program to work with all the pieces.