Apache Solr

Apache Solr is a standalone enterprise search server that indexes data from nearly any source and makes it searchable through a simple HTTP interface. It handles full-text search, faceted navigation, spell checking, hit highlighting, and advanced geospatial queries out of the box. Solr runs on Java and supports replication and sharding for high availability across large clusters.

Solr integrates with databases, content management systems, and web crawlers using its DataImportHandler. It supports RESTful APIs, JSON, XML, and CSV output formats, and includes a built-in admin web interface. The platform powers search for thousands of websites and applications, from ecommerce catalogs to document repositories. Solr's schema can be configured manually or inferred automatically from indexed data.

Orginated from the Apache Lucene project and governed by the Apache Software Foundation, Solr is free and open source under the Apache License 2.0. It runs on any system with a Java runtime, including Linux, Windows, and cloud environments. Adopted by companies like Netflix and eBay, Solr is a mature choice for developers who need scalable search without vendor lock-in.