[Python] Cross platform Python apps

[Rob Hudson]

I've noticed a few, very nice applications that are cross platform and 
are written in Python.  The latest one I found is Democracy Player:

http://www.getdemocracy.com/

Looking at the online source code:
https://develop.participatoryculture.org/projects/democracy/browser/trunk/tv

There is a portable directory with lots of Python, and then individual 
platform directories for platform specific code and front-ends (Cocao 
for OS X, GTK for Linux, XUL for Windows).

How does one learn about creating cross platform applications like this?

Being Python makes it all the more accessible to me.  It leverages other 
open source technologies (VLC, XUL, Bittorrent).  This seems like a nice 
way to go.

Are there general docs or tutorials for making cross-platform apps in 
Python?  Anyone playing with these tools already?

Thanks,
Rob