You can use a database or flat files to simply store information submitted by users....verify that the information conforms to your website submission policy...and then display this information in descending order.
There are many free applications specific to JSP/J2EE technologies and the best place to search for these tools is hot scripts
If server side technology is not an issue, you may wish to have a look at WordPress which is built on MySql and PHP....and can be used as a personal website, blog, etc.
Another well known solution is wikimedia http://download.wikimedia.org/
I would also suggest that you do a google search specific to your requirements..as it is likely that there is an open-source solution for it....where you can do some customizations to meet your specific requirements.