Hurl 4.0.0 is a command-line tool that runs HTTP requests defined in a simple plain-text format, with features such as improved HTML reports, detailed error messages, and custom HTTP methods. The tool is powered by curl and allows users to define requests and assertions in a straightforward way. The new release includes several improvements and bug fixes, making it a useful tool for testing and validating HTTP interactions. Hurl can be used in various CI/CD pipelines and is an alternative to other tools like Postman.