OpenSearchServer is a powerful search engine and crawler with XML/HTTP API, PHP/ASP client. It allows you to create any kind of Search applications: Web search (internet, intranet, extranet), desktop and networked search, portable search for distributing CD/DVD. OpenSearchServer was developed in such a way that you can do all of these things as simply as possible.

Features of OpenSearchServer:
- A crawler allows you to index the following: web pages; rich format documents from files on local and remote systems; and contents from any JDBC database, such as Oracle, MySQL, Microsoft SQL Server,
- Full text analyzers and filters allowing indexing and searches in 16 languages: Chinese, Danish, Dutch, English, Finnish, French, German, Hungarian, Italian, Norwegian, Portuguese, Romanian, Russian, Spanish, Swedish, Turkish.
- Multi-lingual analysers slice sentences into words, then run lemmatisation algorithms on words based on the document’s language (singular/plural, gender, conjugated verbs, etc.)
- HTML renderer allowing the integration of the search box in an HTML/XHTML page, working with PHP and .NET, client library and XML over HTTP API,
- Parsers allowing you to get content and metadata from most documents and formats, such as XML, HTML/XHTML, Adobe™ PDF, Microsoft™ Word™, PowerPoint™, OpenOffice™, RTF, Plain text, Torrent, Audio files (MP3/MP4, OGG, FLAC, WMA) etc.
- A series of caches to accelerate processes and deliver faster applications,
- Monitoring and administration: Alerting services, integrated scheduler, index replication, user management,
- Free online developers' documentation,
- Advanced functionality: faceted search, clustering, filters, snippets, synonyms, stopwords, highlighting, categorization, “find similar”, automatic thumbnail screenshot inclusion, boost/reduce relevance.
- Drupal module and WordPress module available.
- The web interface is built around the Zkoss (ZK) framework.