Inkscape - Inkscape is a free, open source professional vector graphics editor for Windows, Mac OS X and Linux.
Invision - Prototyping and collaboration for design teams
Adobe Illustrator CC - Adobe Illustrator CC is a commercial vector graphics editor.
Moqups - The most stunning HTML5 app for creating resolution-independent SVG mockups, wireframes & interactive prototypes for your next project
Boxy SVG - Boxy SVG is a vector graphic editor built for the modern web.
Balsamiq - Balsamiq. Rapid, effective and fun wireframing software.