Xapian - Xapian is an open source probabilistic information retrieval library, released under the GNU...
DuckDuckGo - The Internet privacy company that empowers you to seamlessly take control of your personal information online, without any tradeoffs.
ElasticSearch - Elasticsearch is an open source, distributed, RESTful search engine.
Google - Google Search, also referred to as Google Web Search or simply Google, is a web search engine developed by Google. It is the most used search engine on the World Wide Web
Kaizen - Kaizen is an ElasticSearch GUI for Windows, Mac and Linux, written in JavaFX as a cross-platform desktop application.
Searx - Open source metasearch engine