Search Engine Abstraction Layer
SEAL Search - Flexible integration of the Search Engine Abstraction Layer project
MK Search
Generic highly adjustable and extendable search engine framework, using Zend Lucene, Apache Solr or ElasticSearch. But support for other search engines can be provided easily.
Apache Solr for TYPO3 - Enterprise Search
Apache Solr for TYPO3 is the enterprise search server you were looking for with special features such as Faceted Search or Synonym Support and incredibly fast response times of results within millisec
Apache Solr for TYPO3 - Result Grouping
Solr Result Grouping allows grouping of documents sharing a common field. For each group the most relevant documents are returned.