EventBuilder is a complex and advanced events responsive WordPress themes. You can now build your own events portal on which users can add events in the categories you define. They can even sell tickets to their events via the Tailor Ticket WordPress Plugin. You setup the pricing plans and get paid via PayPal or by Credit / Debit Cards (Stripe). The registration and login are all front-end, of course There are so many features which probably make Event Builder the most universal events directory theme on the market.
Demo: http://themeforest.net/item/eventbuilder-wordpress-events-directory-theme/11715889