Retool is a development platform that allows organizations to build custom internal tools efficiently. It provides a set of building blocks like tables, charts, forms, and more that users can drag and drop to create custom apps. Retool is designed to connect to a variety of data sources, enabling users to query and update their data directly through the built tools. It is known for its flexibility in helping developers and non-developers alike to quickly build and deploy internal applications without having to write extensive frontend code.