Vector editor Adobe Flash CC alternatives

Question

I'm looking some vector editing tool which can allow me do next drawing:

https://youtu.be/nbyqhru41co

(I made this sketch in 2 minutes with Adobe Flash CC)

Requirements:

• Auto snapping - cursor is snapped to line ending or segment center;
• Easy select part of object - select side of square with one click, select big object with double click, select everything in rectangle selection;
• Auto detect lines intersection;
• Layers support.

Optional requirements:

• OS Windows;
• Free or OpenSource.

I've tried Inkscape but it's hard to use. Can't find how to select part of square, how to detect lines intersection. Can't understand object and path concepts and why do I need to convert one to another?