You don't need other people to swim, but a Microsoft Research project can spice up your swimming routine by putting you in or pitting you against virtual teams. Redmond's research division is working with a team of researchers from Korea Advanced Institute of Science and Technology (KAIST) to develop SwimTrain. It's a system consisting of an app, a waterproof case for your smartphone and a pair of underwater headphones that provides sensory/auditory feedback. SwimTrain puts you in a team of three swimmers -- if you're competing, it tells you how you're doing against your two virtual opponents. If you're in the same team, it helps you maintain your strokes so you can keep up with your virtual teammates.