Exploiting vulnerabilities and taking control of remote computers is a complex and difficult undertaking. Metasploit simplifies things by providing a consistent interface for exploits and allows you to use your choice of payload with your chosen exploit. Features such as sessions and jobs make wide-scale exploitation and automation possible, while encoders and NOP generators make sliding past filters and network security devices as easy as setting an option. Finally, Metasploit's multiple interfaces, from command-line to web interface, makes using Metasploit easy and enjoyable no matter what you are comfortable with.
—Bryan Burns