This has to be the simplest program for anyone who wants to start doing 3D modeling. You simply draw shapes (in 2D) and on a panel beside it, you will see it in a 3D form. Now, you probably aren't going to like it like that, so you can right click any object you made, and adjust things such as height and transparency.
But wait, there's more! In the 3D version of your "masterpiece" you can have light be directed towards a specific spot in your model, and additionally you can change the color of the light. There are many other things you can do, but I will leave you up to explore all of them :) Finally, when you have completed your model, you can export either your 2D or 3D model into a bmp document.
This program may be fun and all, but it definitely has it's limitations. First of all, lets say you want a circle to be on top of a square, well, in this program, it is almost impossible. Unless you use the scripting language that it uses (VRML), you have to have it just right to make it look like something is on top of another thing. Another thing is, there are a lot of commands, but the commands don't give you that much control.
Other than the limitations, there is only one problem with this program. It tends to crash every so often. It doesn't crash that much, but it has crashed on me a total of about 3 times, which is more crashes than the average program should have in my opinion.
In conclusion, if you want to get a feel for 3D modeling, or you just want something to play with when you are bored, I would go ahead and download this. It's only a little over 3MB, and it's free! You can't beat that. Additionally, most people will learn how to use it within minutes, with a manual or not. ;-)