Responsinator - Designed to test responsive websites on different devices.
Axure - The most powerful way to plan, prototype and hand off to developers, all without code. Download a free trial and see why professionals choose Axure RP 9.
SlideRule UX Design Path - Curriculum of Online Courses To Learn UX Design
Balsamiq - Balsamiq. Rapid, effective and fun wireframing software.
BareMetrics - SaaS Analytics for Stripe
Moqups - The most stunning HTML5 app for creating resolution-independent SVG mockups, wireframes & interactive prototypes for your next project