React Proto - React application design and prototyping tool
Marvel - Turn sketches, mockups and designs into web, iPhone, iOS, Android and Apple Watch app prototypes.
UI Bakery - An intuitive visual internal tool builder. Allows you to create admin panels, CRMs, customer support tools on top of your database. Integration with MySQL, PostgreSQL, MongoDB, and more. Add business logic, manage user permissions, share your app.
Ditto for Developers - Sync the latest copy edits from design to development
Invision - Prototyping and collaboration for design teams
Kite Compositor - A powerful animation and prototyping application for Mac & iOS.