The field of search engines is progressing rather rapidly in recent years as they become more and more powerful. Nowadays it is very easy to enable state of the art full-text search in any application using open-source tools like Lucene, Solr or ElasticSearch. This is not about exposing content to Google for indexing; it's about providing your own tailor made search, within your system to your users.

But the coolest thing is this: search engines can be extremely useful even if you don't need full-text search capabilities. A search engine - be it Lucene or ElasticSearch - can be easily used for other cool and very useful things like live analytics or to enhance the user experience of applications. Its not just about full-text search anymore.

Lucene is the biggest and most popular open-source search engine which is also in the heart of other open-source software like Solr and ElasticSearch, both are very popular search servers. Large players like Twitter and LinkedIn are using Lucene for years, and continously contribute code back to the project.