The Mobile Access to Supplementary Learning Objects (MASLO) is an open source software kit developed by the Advanced Distributed Learning Co-Laboratory (AADLC) at the University of Wisconsin-Extension. The MASLO kit is designed to provide the components for content authoring and delivery on Apple iOS® and Google Android® smart phones. This project built on work from an earlier AADLC effort to develop a high school test preparation mobile application called Revu4u (Review for You). In that project, AADLC team members successfully created a technical framework for delivering smart phone enabled instructional content. While the technical components functioned as intended, virtually no time was spent in Revu4u on creating usable interfaces. Additionally, the Revu4u project was limited in scope to only deliver multiple-choice questions and feedback. The MASLO project focused on usability rather than technological capability and was designed as a more comprehensive instructional content authoring environment. In this article, the authors will describe MASLO as a design case. The purpose is to clearly describe the kit itself, critical design decisions, and the context and situations relevant to understanding the decisions made. Relevant Revu4u processes and outcomes are briefly described as a precedent for MASLO. MASLO is a living, open source project, and this case describes the development of the kit up to August 2012.