Failure rates in first year calculus courses are high in most post-secondary institutions across North America and other parts of the world. This Inukshuk-funded open education project involved the development of five stand-alone pre-calculus learning modules. The design and revision phases of this project occurred between the fall of 2007 and late spring of 2009. These modules were designed to support learners enrolled in first year calculus by providing just-in-time instruction in five areas: algebraic operations, factorization, polynomials and rational expressions, radical expressions, linear and quadratic equations. One of the major challenges of the project was developing dynamic activities that could support the display of a variety of mathematical formulas. To this end an open source Flash-based authoring tool was developed called the Athabasca University Tutor Authoring Tool (AUTAT). This paper explores the design and development of the AUTAT based on the needs assessment and design principles discussed.