Weld - Create websites with any design, for any device, for free, including domain.
Figma - Team-based interface design, Figma lets you collaborate on designs in real time.
Invision - Prototyping and collaboration for design teams
Icons8 Lunacy - Free graphic design software with built-in resources. Fully compatible with Sketch and works offline
Marvel - Turn sketches, mockups and designs into web, iPhone, iOS, Android and Apple Watch app prototypes.
Sketch - Professional digital design for Mac.