OpenRocket is a free, fully featured model rocket simulator that allows you to design and simulate your rockets before actually building and flying them. The main features include: Six-degree-of-freedom flight simulation Automatic design optimization Real-time simulated altitude, velocity and acceleration display Staging and clustering support Cross-platform (Java-based) OpenRocket is an Open Source project licensed under the GNU GPL. This means that the software is free to use for whatever purposes, and the source code is also available for studying and extending.