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, the reason being that such tools impose conformity and precision prematurely. Sketching on the other hand is a highly fluid and flexible way of expressing oneself. In this paper, we present Calico, 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 software design. Calico is meant to be used on electronic whiteboards or tablets, and provides for rapid creation and manipulation of design content by sets of developers who can collaborate distributedly.

Despite the availability of a host of software design notations and associated tools, software developers are known to frequently turn to the whiteboard when faced with a specific design problem. There, they typically engage in an informal form of software design that relies heavily on sketching. However, whereas whiteboards afford flexibility and fluidity, they at the same time limit a designer in only being able to draw and erase content. This paper presents Calico, a novel software design tool that leverages electronic whiteboards to enhance the design experience with explicit support for the creative, exploratory aspects of design. Specifically, Calico offers a grid, scraps, and a palette together with gesture-based input to address several natural behaviors exhibited by software designers, including frequent shifts in focus, use of low-detail models, and use of a mix of notations. To evaluate Calico, we performed a laboratory experiment involving eight pairs of graduate students and collected and analyzed six corporate design sessions that employed Calico. Results are promising and indicate the benefits of Calico, while they at the same time highlight several ways in which it can be enhanced.