Sq.io is a free and open-source data wrangling tool that allows users to inspect, query, join, import, and export data from various sources, including databases and documents. It is described as 'jq for databases and documents' and provides a query language called SLQ. The tool supports multiple data formats, including CSV, JSON, and Excel, and can output data in various formats. Sq.io aims to simplify data manipulation and querying tasks.