Inkscape - Inkscape is a free, open source professional vector graphics editor for Windows, Mac OS X and Linux.
UXpin - Design is really about solving problems. UXPin is the UX Design Platform that gets that right.
Sketch - Professional digital design for Mac.
Figma - Team-based interface design, Figma lets you collaborate on designs in real time.
Affinity Designer - Professional creative software, exclusively for Mac.
Moqups - The most stunning HTML5 app for creating resolution-independent SVG mockups, wireframes & interactive prototypes for your next project