Sphinx is a full-text search engine, distributed under GPL version 2.
Commercial licensing (e.g. for embedded use) is also available upon request.
Generally, it's a standalone search engine, meant to provide fast,
size-efficient and relevant full-text search functions to other
applications. Sphinx was specially designed to integrate well with SQL
databases and scripting languages.
Currently built-in data source drivers support fetching data either via
direct connection to MySQL, or PostgreSQL, or from a pipe in a custom XML
format. Adding new drivers (e.g. native support other DBMSes) is
designed to be as easy as possible.
Search API native ported to PHP, Python, Perl, Ruby, Java, and also
available as a plug-gable MySQL storage engine. API is very lightweight so
porting it to new language is known to take a few hours.
As for the name, Sphinx is an acronym which is officially decoded as SQL
Phrase Index. Yes, I know about CMU's Sphinx project.