Fusion 360 is a computer-aided design (CAD) program that is free for personal use, although some of its more advanced capabilities are locked behind a paid subscription. The free version is still a solid and capable platform for mechanical or geometric designs, offering basic simulation of joints and other interactions between assembled components. As a CAD platform, Fusion 360's workflow differs slightly from the two other modeling programs discussed in this wiki. Rather than basing its models on primitive solids (i.e. cubes, spheres, etc.), Fusion 360 works with flat sketches that are then given depth, although beyond that the same principles of building a model from simpler forms still apply.
1. If you have not already done so, you can download Fusion 360 at https://www.autodesk.com/products/fusion-360/free-trial