Diagram Designer is a very simple vector graphics editor and object creator with which you can create charts, diagrams, graphs and sketches of all kinds. It is a freeware diagram designing application that's easy-to-use and well-designed.
Here are some screenshots to illustrate the features and user interface of this application:
Autodesk Design Review
3D Object Converter
LibreCAD
Autodesk 123D Design
Autodesk Fusion 360