Sphinx (search engine)!

Algolia provides a developer-friendly RESTful API for website and app instant search. Most web services and mobile apps, such as Spotify, Salesforce or Amazon need to provide a fast and meaningful access to database objects via a simple search box. People want to find songs, invoices, products in just a few keystrokes.

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

There is no larger compendium of shared human knowledge and creativity than the Commons, including over 1.1 billion digital works available under CC licenses. Despite the tremendous growth of the Commons, and the widespread use of the CC licenses and public domain marks, there is no simple way to maximize use of, and engagement with, all of that content. There is no front door — no tool designed for the general public to facilitate discovery for the purpose of reuse and remix, to simplify the license terms, make attribution easy, or support curation, and crowdsourced metadata. »

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.

Findx is a search engine based in Europe, one that respects your privacy and provides you with unbiased search results.As a European search engine, findx fully complies with European laws and regulations, and is hosted in Europe.

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.

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.

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.

The open source (GPL v3) project strus provides a collection of programs and libraries (language C++) for building a competitive scalable full-text search engine. The search index is distributable and user rights can be implemented.

Unlimited Searching

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.

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.