Qikipedia - Instant Wikipedia summary cards on any web page
Apache Lucene - High-performance, full-featured text search engine library written entirely in Java.
Six Degrees of Wikipedia - Find the shortest path between two subjects
List.js - Tiny, invisible and simple, yet powerful and incredibly fast vanilla JavaScript that adds search...
Newsit - Find the discussion around the page you're looking at!
Butter.ai - Your team has Q’s, Butter.ai has A’s.