OpenSearch is a free self-hosted headless (RESTful) Search engine that you can setup and use privately in your server.
It is a distributed search and analytics engine based on Apache Lucene. After adding your data to OpenSearch, you can perform full-text searches on it with all the features you might expect: search by field, search multiple indices, boost fields, rank results by score, sort results by field, and aggregate results.
It is a community-driven project which started as a fork of Elasticsearch and Kibana (The Data visualization tool), after their license changed.
The project is released under the Apache-2.0 License, which offers more freedom to distribute, modify, and for private and commercial use.