Sphider - Web Spider and Search Engine in PHP

Sphider is a lightweight web spider and search engine written in PHP, using MySQL as its back end database. It is suitable for adding search functionality to small or medium sites (up to 10-20,000 pages).
Compatibility
Sphider is a typical LAMP application (but of course it can also be run under Windows). Sphider was designed to be compatible with older versions of PHP and MySQL, it should work with at least PHP 3 and MySQL 3.23.