WikiBinge - Discover how all things are vaguely connected
Apache Lucene - High-performance, full-featured text search engine library written entirely in Java.
Endless - Random and amazing Wikipedia articles.
Six Degrees of Wikipedia - Find the shortest path between two subjects
Goog3D - Search results powered by Sketchfab 3D previews
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.