cross-platform menubar under Tkinter?

[Russell E. Owen]

Tk (and thus Tkinter) seems to offer the basics for making a menu bar 
for an app that looks reasonable on various platforms (Mac, unix, etc.).

However, it's very low-level and before I reinvent the wheel, I wondered 
if anybody had code that already did the basics, such as:
- figure out if one is on Mac, unix or Windows
- add an "about" command to the appropriate menu (which varies depending 
on platform)
- add an Edit menu with Cut/Copy/Paste whose entries actually do the 
right thing.

and if so, whether I could have a look.

Thanks,

-- Russell