Yioop is an open source, PHP search engine capable of crawling, index, and providing search results for hundred of millions of pages on relatively low end hardware. It can index a variety of text formats HTML, RSS, PDF, RTF, DOC and images GIF, JPEG, PNG, etc. It can import data from ARC, WARC, Media-Wiki, Open Directory RDF. It is easily localized to many languages. It has built-in support for new feeds, discussion groups, blogs, and wikis. It also supports mixing indexes to create mash ups.