Computational techniques and software applications for the quantitative content analysis of texts are now well established, and many qualitative data software applications enable the manipulation of input variables and the visualization of complex relations between them via interactive and informative graphical interfaces. Although advances in text analysis have helped researchers mine text data for semantic content and identify language patterns in text with greater facility, interactional dynamics and patterns of talk have been neglected. This article introduces a new open-source tool, "Interactional Discourse Lab." This tool is designed to map dynamics in spoken interaction and to represent them in easily accessible visual form, capturing aspects such as the frequency and patterning of exchanges, and the distribution of turns and discourse features. It is designed to contribute, with other analytical tools such as those used in text analysis, to the development of "interactional topographies." The paper sets the tool within a wider case for the development of open-source software in applied linguistics as a platform for methodological innovation.