If you're looking for a more “serious” CAD package without paying “serious” money, check out OnShape and Fusion 360. Both of these packages are industrial-strength CAD (parametric, history-based, and constraint-solving) and can be used for free.

OnShape (https://www.onshape.com/) has a frontend that runs entirely in the browser on the desktop, so you can even run it on Linux, and has apps with real create/edit capability for phones and tablets.

If OnShape doesn't have everything you want, or you run into its storage limits and don't want to pay for more space, check out Fusion 360. It's free for hobbyists. It only runs on Mac and Windows, but it's got a ton more features than OnShape and no storage limits.

I played with Fusion 360 before I found OnShape and wasn't able to make much headway, even after checking out some of Autodesk's training videos. When I found OnShape, I watched its training videos and got a handle on the basic CAD concepts. When I ran into OnShape's limits, I was able to go back to Fusion 360 and understand it. Now I use Fusion 360 to design parts for hobby-level 3D printing and it's great.