Sphinx is a full-text search engine, publicly distributed under GPL version 2. It was specially designed to integrate well with SQL databases storing the data, and to be easily accessed by scripting languages.
Technically, Sphinx is a standalone software package provides fast and relevant full-text search functionality to client applications.
However, Sphinx does not depend on nor require any specific database to function.
Applications can access Sphinx search daemon (searchd) using any of the three different access methods: a) via Sphinx own implementation of My SQL network protocol (using a small SQL subset called Sphinx QL, this is recommended way), b) via native search API (Sphinx API) or c) via My SQL server with a pluggable storage engine (Sphinx SE).
Official native Sphinx API implementations for PHP, Perl, Python, Ruby and Java are included within the distribution package.