Apache Lucene - High-performance, full-featured text search engine library written entirely in Java.

Bandlab - Capture, nurture, and collaborate on song ideas in the cloud

Six Degrees of Wikipedia - Find the shortest path between two subjects

Amper Music - Artificial intelligence music composer

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.

DeepJ - AI-composed piano music in real time