Extract from article by Miles Kehoe
The benefit — and the drawback — with Lucene and Solr is that they are single purpose tools. This is a common issue in the world of open source. While the Apache Project has many supporting tools, such as the Nutch crawler and the Tika “filter pack,” which extend the capabilities of both Lucene or Solr, implementing a pure open source search solution takes significant effort.
It only made sense that companies would form to both assist implementing Lucene and Solr; and the same companies would benefit by providing support, services, and products that extend the capabilities of the open source technology.
A few examples? Solr is the technology under Lucidworks Fusion. And Lucene, the kernel on which Solr is based, drives Elasticsearch and the enterprise search tool Swiftype, which is now part of Elasticsearch.