Create a directly-executable cross-platform GUI app using Python

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 (popular, free for commercial projects)
• Qt using the PyQt bindings or Qt for Python. The former is not free for commercial projects. The latter is less mature, but can be used for free.

Complete list is at http://wiki.python.org/moin/GuiProgramming

Single executable (all platforms)

• PyInstaller - the most active(Could also be used with PyQt)
• fbs - if you chose Qt above

Single executable (Windows)

• py2exe - used to be the most popular

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

Another system (not mentioned in the accepted answer yet) is PyInstaller, which worked for a PyQt project of mine when py2exe would not. I found it easier to use.

http://www.pyinstaller.org/

Pyinstaller is based on Gordon McMillan's Python Installer. Which is no longer available.