Elasticsearch
Distributed search engine built on Apache Lucene — Shay Banon, 2010 (Elastic NV). RESTful API, JSON documents, near-real-time indexing.
Powered the ELK stack (Elasticsearch + Logstash + Kibana, today the Elastic Stack). Aggregations also make Elasticsearch an analytical database. Sharding + replication are automatic. Modern Elasticsearch (8+) has built-in vector search for RAG.
In 2021 Elastic switched the licence to SSPL/Elastic License, which triggered Amazon's fork → OpenSearch. Today they coexist but the ecosystem is split.