MathJax is a modular javascript framework for including mathematics in web pages. It can take input in various formats, like TeX and MathML, and can produce output in various forms, such as MathML or HTML-with-CSS. Components are loaded as needed.
Gravity Board X is forum software written in PHP and MySQL. GBX features a unique front page layout, and version 2.0 will push the envelope with features such as a CSS-based layout, WYSIWYG message editor and AJAX framework.