I've been playing with both OnShape and Fusion 360 recently. Previously I've used things like TurboCAD for 2D drawing and although I've tried using the 3D features, I've found it very difficult to use. These two new tools are a breath of fresh air. I'm sure that long-term professional users will know all this already, but if you've never tried it, the sketch-and-extrude, parameter-based approach makes things much easier to draw and much easier to modify and update. On balance, OnShape is probably the easier to use as they have worked hard at simplifying the user interface while F360 is a better established and more powerful tool. F360 also has the "sculpt" tools for more fluid shapes (might be what Washout was referring to) although I've stuck to just the straightforward geometric tools so far. It's been useful for both mechanical engineering type drawings (my new router is being drawn in F360 as it gets built) and for models for 3D printing.

It's difficult to describe the difference in approach between conventional 2D CAD and these newer applications, but it's a bit like the difference between a power-assisted old-fashioned drawing board, and the ability to scribble on the back of an envelope, add a few dimensions, and watch the 3D structure appear in all its glory. Hit a couple of buttons and 3D objects appear as a set of 2D drawings, ready for manufacture. Can't believe that applications like this are available free to the hobbyist.