Katla is a user generated content theme for WordPress made by Bluthemes.
It offers the ability for users to submit content to your website via a custom made form. All the submitted posts are inserted as pending posts so a moderator can review the submission and do any changes if necessary.
Once the submission has been reviewed a moderator can publish the post on the website.
Posts on the website can then be up or down voted by users. The theme includes a special “Popular posts” page template which you can use to show what posts are trending at the moment.
The algorithm works similar to how sites like Reddit order content by popularity.
The theme also offers a simple but powerful theme options page where you can change multiple aspects of the design and functionality with a click of a button. All options are thoroughly explained so even the novice WordPress users will have no issue working with it.