UMLGraph - UMLGraph is a professional automated drawing tool that allows the designers the declarative specification and drawing of UML class and sequence diagram.
Cadbull - Cadbull is a website that comes with an advanced collection of CAD blocks and DWG design, facilitating architects and designers to get done with their projects efficiently.
yEd - yEd is a free desktop application to quickly create, import, edit, and automatically arrange diagrams. It runs on Windows, Mac OS X, and Unix/Linux.
DWGFREE - DWGFREE is an online platform that comes with a comprehensive collection of CAD blocks that can be downloaded without the need for registration.
Dia - Dia is a GTK+ based diagram creation program for GNU/Linux, MacOS X, Unix, and Windows, and is released under the GPL license.
RealityMAX - RealityMAX is the most powerful free 3D design collaboration platform, 100% online. Cooperate remotely with your colleagues on 3D projects and easily share your work with clients. Create Web3D and AR experiences in a snap, without a line of code.