It's a PHP/MySQL based search engine that has quite a few nifty little features. There is a free lite version and a professional version for 19.99 (limited time offer). Here is a short description (check the URL for full list of features and an online demo):
SearchSite is a richly-featured PHP search engine that uses MySQL as the database backend. This small, but powerful search engine is ideal for almost any web site. Not only can it index and search by meta data, page content, and titles, but allows for unlimited searches to be setup to index various web pages and portions of your site. Search results can be customized to suit your site's needs through the use of templates driven by CSS styles. Setup and configuration is a breeze through an online password-protected web page.