There are many CAD softwares, many of which are free for students and educators. We will be going over the most popular free CAD softwares.
The Big Three
Autodesk Fusion 360
Autodesk Fusion 360 is free for students, educators, and educational institutions, and free for one year for hobbyists. It is available for Windows and Mac users. Our team uses Autodesk Fusion 360 for our design process and have developed a love-hate relationship. Fusion 360 is cloud-based which makes things slow sometimes, but there are many features that make the experience amazing. In general, we would recommend Autodesk Fusion 360, especially for hobbyists, and we even teach summer CAD courses [link] using Fusion 360.
Solidworks is a popular CAD software. It is only free for students, it's harder to get the student licence, and is only available for Windows. Since it is unavailable on Mac, our team can't use it. It has similar and better features compared to Autodesk Fusion 360 and was the former CAD software used by Tesla before they switched to the more complex Catia. We realize that our viewpoint on Solidworks may be biased because of our general lack of experience with it, so check out this amazing article.
Just like Solidworks, Autodesk Inventor is only available on Windows, which makes it harder for us to recommend. However, several members of our team who have learned Autodesk Inventor at school rave about it's features that Autodesk Fusion 360 doesn't have. It is much more industrial in many regards and can handle more complicated and specific details.
CAD for Art
If you are looking to use CAD to create art, Blender is the go-to recommendation. It is completely free with loads of features for you to create realistic and aesthetic renders and animations. We use Blender to render our robot to look cool, but we are nowhere near Blender experts. Blender includes physics simulations to animate realistic explosions, and CGI tools for you to create movie shots, to name a few awesome features. The scale leads to a very steep learning curve, but the massive online Blender community has many tutorials and forums to help you out. However, we would not recommend Blender for industrial physical 3D design purposes.