Stella is one of the programs available to model systems. It is created by High Performance Systems, Inc. This software has allowed many high school students to be able to learn about system dynamics. Many high school programs use Stella to teach their students about system dynamics. Before Stella came out, students weren't given the opportunity to learn about system dynamics until they were in graduate school. Now, students have the chance to learn about system dynamics at certain high schools. The current version is Stella 8, new users can download a save-disabled trial version here.