Indexer4j

Apache Solr

Enterprise search platform featuring full-text search, hit highlighting, faceted search, real-time indexing, dynamic clustering, and rich document (e.g., Word, PDF) handling. (Source Code) Apache-2.0 Java/Docker/K8S

Apache Lucene

High-performance, full-featured, cross-platform, text search engine library

Elasticsearch

Distributed, multitenant-capable, full-text search engine with a RESTful web interface and schema-free JSON documents