MongoDB - MongoDB (from "humongous") is a scalable, high-performance NoSQL database.
Doxygen - Generate documentation from source code
PostgreSQL - PostgreSQL is a powerful, open source object-relational database system.
DocFX - A documentation generation tool for API reference and Markdown files!
ElasticSearch - Elasticsearch is an open source, distributed, RESTful search engine.
Natural Docs - Natural Docs is an open-source documentation generator for multiple programming languages.