Metasploit works on Linux and Windows only.

You can download it at www.metasploit.com

A security specialist would use metasploit to determine that a change to their software was working correctly by developing a test that Metasploit could use repeatedly to test the solution.

Put simply, Nessus identifies potential vulnerabilities, whereas Metasploit exploits the vulnerability. Metasploit is basically a list of exploits you can use against a target, Nessus tells you which one you should pick a bit like asking a shop assistant what would work best to hack the said computer, the shop assistant (Nessus), will say: "Yes of course sir, I think you will want this." as he points to an item on the shelf (Metasploit).

Exploit is a computer security software. Exploit helps protect a site from being attacked by bugs and glitches. An exploit can take over a computer system, and the software "Exploit" helps protect against that.

Exploited is the past tense of exploit.