Arachni-web on Kali Linux

apt-get update
apt-get install arachni

Intro - Arachni is an Open Source, feature-full, modular, high-performance Ruby framework aimed towards helping penetration testers and administrators evaluate the security of web applications.
1. How to open
A. GUI Method
Application → Kali linux→ Web Applications → Web Vulnerability Scanners → arachni-web

Fire up your Firefox and do a 
*Note: There are some instance where arachni will provide a different port. Look at the output
>>>Listening on (this is where it will show what port it is using)

You need to sign in and by default, the user name and password are inside the 'README' file

Read the 'README' file by doing a 
#less README

Input the credentials and you are now ready to use Arachni!