Open Source Scripts
Have you ever come across a scrip that did everything you wanted and you just had to have it? Some of those scripts can cause hundreds of dollars, luckily the open source world is here to help. Most scripts you find on the internet have an open source alternative.
Content Management Systems
There are many open source cms scripts available online. A couple of the most popular scripts are Joomla and Drupal. These scripts allow you to control the content on your website using a What You See is What You Get (WYSIWYG) editor. They also have many addons available like login controls, forums, blogs, and a great variety of web 2.0 scripts.
eCommerce
osCommerce, Zen Cart, and up and coming Magento are some of the biggest open source ecommerce scripts available at the moment. These great scripts allow you to create your own ecommerce website managing unlimited products, payment and shipping integration, and much more.
Blog
Wordpress is the best free blogging software available at the moment, although there are more.
Do a Google search for open source scripts and you will find many available.