In 2014, while working on a Scala-based CMS - Content Management System - with an integrated search engine based on Elasticsearch, I found myself using the Elastic4s open-source project. And as it often happens, not all our use-cases were covered by the existing features, so I contributed a few new features.
See all my contributions.
At some point I also became a committer on the project.
While I don't use this project anymore, it is still alive and used by companies such as Barclays Bank, HSBC, Shazaam, Deutsche Bank, Goldman Sachs, Canal +, Soundcloud, …
Project link: https://github.com/sksamuel/elastic4s