Marvel - Turn sketches, mockups and designs into web, iPhone, iOS, Android and Apple Watch app prototypes.
Piktab - Discover free graphic resources on every new tab
Ditto for Developers - Sync the latest copy edits from design to development
prototypr.io - Daily design news, inspiration and deals
Kite Compositor - A powerful animation and prototyping application for Mac & iOS.
Design Hunt - Curated design inspiration for everyone