Apache Lucene - High-performance, full-featured text search engine library written entirely in Java.
Geocode Earth - Build smarter location experiences with our fast, accurate & affordable geocoding solutions.
Six Degrees of Wikipedia - Find the shortest path between two subjects
Mapbox - An open source mapping platform for custom designed maps. Our APIs and SDKs are the building blocks to integrate location into any mobile or web app.
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.
OpenCage Geocoder - Easy, Open, Worldwide, Affordable Geocoding.