1. SketchUp Make
SketchUp Make is the most widespread free general use CAD software. You can use it for 2D and 3D designs and has amazing capabilities. It is even better that about generic CAD software such as AutoCAD and Microstation. It aslo hase a huge library, called 3D Warehouse, where users and manufactures contribute with millions of ready to use 3D objects. You can download the software here http://www.sketchup.com/products/sketchup-make
Unrestricted freeware, Windows XP / Vista / 7 / 7 64 bit / 8 / 8 64 bit. Not allwed to use for commersial purposes
http://librecad.org/ is a fully comprehensive 2D CAD application that you can download and install for free. There is a large base of satisfied LibreCAD users worldwide, and it is available in more than 20 languages and for all major operating systems, including Microsoft Windows, Mac OS X and Linux (Debian, Ubuntu, Fedora, Mandriva, Suse ...).
Design for Mechanical engineer. Good qualiry 3D parameteric design. Highly recommened http://www.freecadweb.org/
5. KiCad EDA
A Cross Platform and Open Source Electronics Design Automation Suite. With the schematic editor you can create your design without limit; there are no paywalls to unlock features. An official library for schematic symbols and a built-in schematic symbol editor help you get started quickly with your designs.
7. Sweet Home 3D
Για 3D αρχιτεκτονικό σχεδιασμό http://www.sweethome3d.com/ an application that helps you place furniture on a house 2D plan, with a 3D preview.