UXpin - Design is really about solving problems. UXPin is the UX Design Platform that gets that right.
Marvel - Turn sketches, mockups and designs into web, iPhone, iOS, Android and Apple Watch app prototypes.
Figma - Team-based interface design, Figma lets you collaborate on designs in real time.
Invision - Prototyping and collaboration for design teams
Moqups - The most stunning HTML5 app for creating resolution-independent SVG mockups, wireframes & interactive prototypes for your next project
Pencil - Pencil is an animation/drawing software for Mac OS X, Windows, and Linux.