Software designers frequently sketch when they design, particularly during the early phases of exploration of a design problem and its solution. In so doing, they shun formal design tools, opting for the whiteboard of pen/paper instead.  Calico is a sketch-based distributed software design tool that supports software designers with a variety of features that improve over the use of just pen-and-paper or a regular whiteboard, and are tailored specifically for early software design on tablets and electronic whiteboards.