Algolia Places - Intelligent address autocomplete for any <input>
Apache Lucene - High-performance, full-featured text search engine library written entirely in Java.
Qikipedia - Instant Wikipedia summary cards on any web page
Six Degrees of Wikipedia - Find the shortest path between two subjects
Search Later - Save interesting article keywords to Google them later 🤓
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.