One of the most-frequently asked questions of all time is this: "I have a Python application I've developed; how do I deliver it to my customer/friend/...?"
Here are typical answers:
tar up the source and send it. It's reasonable to expect that the end-user's host will have Python installed. MacOS comes that way; most Linux distributions do; and it's not onerous to insist that a Windows user install, for example, ActivePython;
for Windows, use MovablePython;
for this purpose, Pyrex can be regarded as a language variant to Python itself;
py2app is for Macintosh
PyInstaller (supports Windows, Linux and soon Mac)
Esky (adds a bootstrap executable and allows to auto-update your applications over the network or from local directory; supports Windows, Linux and Mac)
FredrikLundh discussed some of these in 2003.
As of 2007, py2exe perhaps is second in use only to source distribution.