Marcin asks "I was considering Blender. Can HeeksCAD do better?"
I haven't tried Blender for a while.
I like to think that HeeksCAD is easier to use, but that might just be because I wrote it.
Here is a video of me playing with HeeksCAD a few minutes ago.
HeeksCAD has plenty of bugs, but it is OK for making some solid models.
It doesn't do anything nice like fitting solids together.
Save the file every time you do something, preferably with a different file name each time, in case HeeksCAD crashes.