If you're a small business person, or a society webmaster, Joomla! may be of interest:
"Joomla! is a powerful free Open Source Content Management System for building professional web sites easily. It is often the system of choice for small business or home users who want a professional looking site that's simple to deploy and use. Joomla! is different from the normal models for content management software. For a start, it's not complicated. Joomla! has been developed for everybody, and anybody can develop it further."
author: Open Source Matters, Inc.
required: Win2K, WinXP, Vista,
size: 5.3 m
BTW, always use your anti-virus, anti-spyware software to check downloads before installing-- better safe than sorry!