Arachni is a comprehensive, modular, and high-performance framework built in Ruby, designed to assist penetration testers and system administrators in assessing the security of contemporary web applications. It is available at no cost, with its source code accessible for public examination. This framework is compatible with multiple platforms, including all major operating systems like MS Windows, Mac OS X, and Linux, and it is distributed in portable packages that enable immediate deployment. Its flexibility allows it to accommodate various scenarios, from a straightforward command-line scanning tool to a vast, high-performance grid of scanners, as well as a Ruby library for conducting scripted audits and a multi-user platform for collaborative web scanning. Moreover, its straightforward REST API simplifies integration with other tools and systems. Additionally, the built-in browser environment enables it to handle complex web applications that utilize advanced technologies such as JavaScript, HTML5, DOM manipulation, and AJAX seamlessly. Arachni's extensive capabilities position it as a valuable asset in the cybersecurity toolkit of professionals striving to secure web applications effectively.