The United Network for Organ Sharing (UNOS) has been using simulation models for over two decades to guide the evolution of organ allocation policies in the United States. UNOS kidney simulation model (KPSAM), which played a crucial role in the 2014 U.S. kidney allocation policy update, is also available to the general public as an executable file. However, this format offers little flexibility to its users in trying out different policy proposals. We describe the development of a discrete-event simulation model as an alternative to KPSAM. It is similar to KPSAM in incorporating many clinical and operational details. On the other hand, it offers more flexibility in evaluating various policy proposals and runs significantly faster than KPSAM due to its efficient use of modern computing technologies. Simulated results closely match actual U.S. kidney transplantation outcomes, building confidence in the accuracy and validity of the model.