Inbound.org is entirely dependent on user contributions and user curation. It uses a Reddit-like system of upvoting to surface the best content to the “hot articles” list on the front page. Anyone with a Twitter account can register for an inbound account (inbound uses Twitter OAuth verification). Account owners can submit new content, as well as vote and comment on submitted content.
Obviously there will be a temptation to spam or game a site this open, but just like on Reddit, inbound has moderators (at this point that appears to be limited to Rand and Dharmesh) who promise to ban anyone who frequently submits bad content or doesn’t act “cool” on the site.