Wonder for Slack - Remember the things your team forgets
Apache Lucene - High-performance, full-featured text search engine library written entirely in Java.
Read Something Great - A fun tool to help fix your information diet.
Six Degrees of Wikipedia - Find the shortest path between two subjects
Qikipedia - Instant Wikipedia summary cards on any web page
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.