Arachni is an open source powerful Ruby framework that allows you to evaluate the security of modern web applications. It supports all major operating systems (Windows, Mac OS X, and Linux), and is distributed via portable packages which allows instant deployment.

It is versatile enough to cover a great deal of use cases, ranging from a simple command line scanner utility, to a global high performance grid of scanners, to a Ruby library allowing for scripted audits, to a multi-user multi-scan web collaboration platform. In addition, its simple REST API makes integration a cinch.

And, due to its integrated browser environment, it can support highly complicated web applications which make heavy use of technologies such as JavaScript, HTML5, DOM manipulation and AJAX.

It is definitely a great addition to your hacking arsenal.