Elasticsearch is a flexible and powerful free / libre / open source, distributed, real-time search and analytics engine. It is super fast, RESTful, based on Apache Lucene and has a very high activity level: https://www.openhub.net/p/elasticsearch
It is part of “The Elasticsearch ELK Stack”. The two other apps of the stack are:
It is also part of WikiSuite (formerly called Tiki Suite)
Assumption: you want to use Elasticsearch for data on a ClearOS instance to index data on the same server (ex.: with WordPress, Tiki Wiki CMS Groupware, etc.). To have a more advanced setup (ex.: a cluster), please refer to the Elasticsearch documentation.
This will later be added to the marketplace. For now, you can install the app via command line: http://wikisuite.org/How-to-install-Elasticsearch-on-ClearOS (from that page, you can also install Kibana)