LucidChart - LucidChart is the missing link in online productivity suites. LucidChart allows users to create, collaborate on, and publish attractive flowcharts and other diagrams from a web browser.
Inkscape - Inkscape is a free, open source professional vector graphics editor for Windows, Mac OS X and Linux.
draw.io - Online diagramming application
Sculptris - Sculptris: Enter a world of digital art without barriers.
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.
ShapeShop - ShapeShop is an advanced and professional 3D design and modeling application that comes with an easy-to-use and user-friendly interface.