Answering Question Papers

I am sure I have spent a decent amount of time searching for a solution for my problem. Here it is.
I run a site for students doing their professional degree. Now I want to add a site where I can post the Previous exam question paper and let the students answer them. Let me tell you that it is not a test where they need to answer. Here, answering the question will be open to all and the best answer will be chosen by vote.
I found most of the plug-ins for conducting tests or exams but here I want to post the questions and let all the people answer.
Does anyone know a plug-in or a theme which will help me do this will be great.
Thank you.
APJ