Wiki says:
Elasticsearch is a search engine based on the Lucene library. It provides a distributed, multitenant-capable full-text search engine with an HTTP web interface and schema-free JSON documents. Elasticsearch is developed in Java and is dual-licensed under the source-available Server Side Public License and the Elastic license, while other parts fall under the proprietary (source-available) Elastic License. Official clients are available in Java, .NET (C#), PHP, Python, Ruby and many other languages. According to the DB-Engines ranking, Elasticsearch is the most popular enterprise search engine.
I love opened and federated technologies, so I was looking for opened social network. I wanted someting that works the same as E-mail does. Everybody can choose if his E-mail account will be hosted on Gmail or for example on Yahoo or if he builds his own E-mail server. Because it doesn't matter where man signs up. Message from user on one provider will find it's way to to mailbox of other user on different provider.