Arachni is a Ruby framework that allows administrators and penetration testers to evaluate the security of modern web applications. It is modular, feature-rich, and high-performance. It is free and open-source, so you can review the source code. It is multi-platform and supports all major operating systems (MS Windows OS X, Mac OS X, and Linux). It is distributed via portable packages that allow for immediate deployment. It can be used for a variety of purposes, including a command-line scanner utility, a global high-performance grid of scanners, a Ruby library that allows for scripted audits, and a multi-user multiscan web collaboration platform. Its simple REST API makes integration easy. It can also support complex web applications that make heavy use JavaScript, HTML5, DOM manipulation, and AJAX thanks to its integrated browser environment.