Apache Solr is an ultra-fast open-source search platform, built on Apache Lucene. It leverages Lucene's full-text, vector and geospatial search capabilities to offer a multi-modal engine applicable to a wide variety of data types.

Solr provides distributed indexing, replication, load-balanced querying, failover and automatic recovery, as well as centralized configuration. Among its hundreds of features: advanced querying and facets, rich content management, spatial search, statistics and aggregations, a plugin system, SolrCloud scaling infrastructure, and an administration interface.

It serves both large-scale deployments — it 'powers some of the most visited sites and applications in the world' — and smaller projects, while remaining accessible.