This Pathways to Enable Open-Source Ecosystems (POSE) project focuses on the development of the Distributed Open Education Network (Doenet), an open-source ecosystem (OSE) designed to facilitate the development, sharing, and classroom use of richly interactive mathematics activities. Through a data-driven education technology platform, Doenet assists educator4s in creating instructional tools for engaged learning and supports educators and researchers in generating new knowledge about the effectiveness of interactive mathematics applications. The research on how Doenet and its freely available tools can deepen a student’s understanding of mathematics will inform the design of future math curricula while increasing access for all students to online activities and curricula. This POSE project allows researchers to run learning experiments on Doenet, while also developing a sustainable model for the Doenet OSE and its growing community of users. The foundation of Doenet is its platform-agnostic semantic markup language DoenetML, which allows authors to express mathematical ideas using an easily learned syntax similar to HTML. Unlike educational Java and Flash applets that were written a decade ago and are no longer supported by modern browsers, content written in DoenetML is not locked into a particular implementing programming language contributing to the potential longevity of the OSE. The expansion of Doenet has four primary components: 1) developing complete course offeri