the system Requirement page has a mistake on website
its says somewhere mysql instead of mongodb..and viceversa...and website does have contact us/feedback page.
MongoDB database (main storage back-end)
MySQL 5.X database (optional, but Similar Questions feature will not work without it)
The reason for this is that MongoDB does not have a full text search feature and we need it in order to find 'similar' questions as well as using it for the search feature)
We use MySQL only for it's full text search and only to index/search question titles.