I wrote a diff and merge program in Python using the Tkinter UI framework.
Running it on OS-X there are two problems:

when starting it the window does not get displayed unless switching back and forth with other running apps. There has been a thread here recommending
top.call('wm', 'attributes', '.', '-topmost', '1')
which is no solution since it keeps the window on top of all - always.
Other say that when packaging with py2app this behavior goes away - I tried and it does not!
There is no way to change the Menu - The first entry is dictated by TK, so the first 
"About xxx" does bring up the TCL credits and can not be replaced with my own apps about info.

So my Idea was to make a cocoa app window wich displays on start and on top and I can define what is in the menu - and integrate the Tk frame with my Python code somehow.
Is that possible?
Try some variant of this command: 
self.createcommand('tkAboutDialog', self.aboutProgram)
and put your app "about" dialog code in the aboutProgram() function.
use a Tkinter frame in a Mac Cocoa app