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ElasticSearch is a distributed, RESTful, free/open source search server based on Java and under the Apache License ( Lucene ).

Solr is an open source enterprise search server based on Lucene search library, with XML/HTTP and JSON APIs. Its major features include powerful full-text search, hit highlighting, faceted search, dynamic clustering, database integration, and rich document handling. Providing distributed search and index replication, Solr is highly scalable.

The easiest way to add great search to your website

Expertrec site search engine helps you add ultra fast search to your website . It adds a superb autosuggest and search listing pages where people can find products with a few keystrokes. Along with this you get complete control over your search results with complete merchandising options and access to real time search analytics.

The best site search for any website. Simple type, get search suggests, autocompletions and structured data at your fingertips.

Xapian is an open source probabilistic information retrieval library, released under the GNU General Public License (GPL). It is a full text search engine library for programmers. It is written in C++, with bindings to allow use from Perl, Python, PHP, Java, Tcl, C#, Ruby, and Lua. Xapian is highly portable and runs on Linux, Mac OS X, FreeBSD, NetBSD, OpenBSD, Solaris, HP-UX, Tru64, IRIX, Microsoft Windows, GNU Hurd, and OS/2.

OpenSearchServer is an open source application server allowing development of index-based applications like search engines. Main features of OpenSearchServer are : An integrated crawler for databases, web pages and rich documents; a user friendly GUI allowing development of most applications with some clicks through an interface built in Zkoss; snippets; faceting; an html renderer for integrating search results in a page; and monitoring and administration features.

With Google Custom Search, add a search box to your homepage to help people find what they need on your website.

Whoosh is a fast, featureful full-text indexing and searching library implemented in pure Python. Programmers can use it to easily add search functionality to their applications and websites. Every part of how Whoosh works can be extended or replaced to meet your needs exactly.

Cludo is a powerful search solution to your website. It is built on top of Elasticsearch which means you do not have to do any further developing, or hire any developer concerning site search. Cludo's focus is to deliver an easy to use search engine with the greatest support and tools.

Measured Search provides a fully-managed personalized search & discovery service offering feature packed textual & relevance based search, contextualized recommendations combined with search & interaction analytics that enable you to increase conversions, interactions & user-satisfaction.

The goal of ItemsAPI is creating search application without spending time for backend. You just provide json data and your backend is ready to go.

Azure Search makes it easy to add powerful and sophisticated search capabilities to your website or application. Quickly and easily tune search results and construct rich, fine-tuned ranking models to tie search results to business goals. Reliable throughput and storage provide fast search indexing and querying to support time-sensitive search scenarios.

SearchBlox is an out-of-the-box Enterprise Search Solution built on top of Apache Lucene/Solr. It is fast to deploy, easy to manage and available for both on-premise and cloud deployment.