What is the function of the Nessus Bridge?

Please address the following
1.    Metasploit Project has created Metasploitable to work in conjunction with Metasploit. What is Metasploitable? The following reference may be of assistance
o    Moore, H. D. (2012, May 31). Metasploitable 2 exploitability guide (Links to an external site.)
2.    What is the function of the Nessus Bridge?
3.    What is the Exploit Database? The following reference may be of assistance
o    Offensive Security. (n.d.). The exploit database (Links to an external site.)
4.    Why is post exploitation included in Armitage? A helpful reference could be the following:
o    Offensive Security. (n.d.). Armitage post exploitation (Links to an external site.)
5.    What is a strategy for penetration testing using Metasploit, to improve data center security?