Apache Lucene - High-performance, full-featured text search engine library written entirely in Java.
PIPL Professional People Search Engine - PIPL professional search is used to find the person behind an email,phone or social profile and covers over 3 Billion people worldwide.
Sphinx Search - Sphinx is an open source full text search server, designed with performance, relevance (search quality), and integration simplicity in mind. Sphinx lets you either batch index and search data stored in files, an SQL database, NoSQL storage.
WikiGalaxy - Explore wikipedia in 3d
OpenSearch - OpenSearch is a community-driven, open source search and analytics suite derived from Apache 2.0 licensed Elasticsearch 7.10.2 & Kibana 7.10.2. It consists of a search engine daemon, and a visualization and user interface, OpenSearch Dashboards.
Wikiwand - A beautiful new interface to Wikipedia