Balsamiq - Balsamiq. Rapid, effective and fun wireframing software.
Plant - Version control app and plugin for Sketch
Invision - Prototyping and collaboration for design teams
Zeplin - Collaboration app for UI designers & frontend developers
FOLIO - Simple version control app for designers based on Git
Moqups - The most stunning HTML5 app for creating resolution-independent SVG mockups, wireframes & interactive prototypes for your next project