Nautilus is a SQL query development tool started in 2009 that is still under development. It helps users understand query results by answering questions about why tuples are or aren't received. It uses various algorithms like TedNaive, TedRevised, and NedExplain, which are open source code implemented in Java as an Eclipse plugin. The tool has over 28,000 lines of code and 230 classes, and relies on dependencies like PostgreSQL, ZQL, and various Java libraries. It is developed by a team that has included past contributors and is currently worked on by Katerina Tzompanaki and Alexandre Constantin.