Sphider is a great product for large sites wanting a free site search product that is scalable and free.

Configuration of this product is extremely simple and it uses a MySql database and php program to index your site as often as you would like. A cron entry can be used to automate the entire process.

If you have a large site and don't have it completely indexed this product will provide everything you need to create a customizable site search facility.

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