It's been a long standing belief with me that computers are way underutilized. People spend too much time aimlessly browsing the web and responding to stupid stuff on social media but not enough time actually doing anything productive with their computers. I want to be an exception to that rule, so I've been teaching myself 3D modeling using a few different programs: Blender, Wings3D, and OpenSCAD.
Blender and Wings3D allow you to fully interact with your 3D graphics using your mouse. You've probably already heard of Blender. Wings3D does basically the same thing, but has less features. It may also be easier to learn.
OpenSCAD is unlike the other programs in that you don't create things graphically. Instead, you type code in a special language. This is great for parametric designs that are alterable by just changing a few variables. Also, it allows for great precision. I highly recommend this program, even to beginners, who might initially be scared of typing code. It's not as hard as it at first seems.
Here are a few screenshots:
