Endless - Random and amazing Wikipedia articles.
Apache Lucene - High-performance, full-featured text search engine library written entirely in Java.
Wiki Reverse - See what websites are linking to Wikipedia pages
Six Degrees of Wikipedia - Find the shortest path between two subjects
Pathica - Find a path to connect with anyone on Instagram.
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.