If YouTube and Instagram had a kid together, it would look an awful lot like Viddy. Members use the site’s iPhone app to shoot and upload brief videos — popular ones often involve animals, kids or breathtaking scenery — but you can watch their clips and follow the most interesting users on the Web. The site even has its share of celebs, including Katie Couric, Jessica Alba and Snoop Dogg. Nothing here is more than a few seconds long, so having a short attention span is a virtue.