If you have running buddies, you know the advantages they bring -- they'll encourage you to run when you'd otherwise slack off, or when you just have to one-up a friend. And Runkeeper knows it. The Asics-owned developer has updated its Android and iOS apps with a Running Groups feature that, unsurprisingly, promises to keep you off the couch. As many as 25 people can participate in challenges (such as distance or the most runs), and there's a group chat to either motivate your pals or trash-talk them when you emerge triumphant.