<s>[INST] How can I create a directly-executable cross-platform GUI app using Python? Python works on multiple platforms and can be used for desktop and web applications, thus I conclude that there is some way to compile it into an executable for Mac, Windows and Linux.
The problem being I have no idea where to start or how to write a GUI with it, can anybody shed some light on this and point me in the right direction please? [/INST] First you will need some GUI library with Python bindings and then (if you want) some program that will convert your python scripts into standalone executables.
Cross-platform GUI libraries with Python bindings (Windows, Linux, Mac)
Of course, there are many, but the most popular that I've seen in wild are:

Tkinter  - based on Tk GUI toolkit (de-facto standard GUI library for python, free for commercial projects)
WxPython - based on WxWidgets (very popular, free for commercial projects)
PyQt - based on Qt (also very popular and more stable than WxWidgets but costly license for commercial projects)

Complete list is at http://wiki.python.org/moin/GuiProgramming
Single executable (Windows)

py2exe - Probably the most popular out there (PyInstaller is also gaining in popularity)

Single executable (Linux)

Freeze - works the same way like py2exe but targets Linux platform

Single executable (Mac)

py2app - again, works like py2exe but targets Mac OS

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