Marvel - Turn sketches, mockups and designs into web, iPhone, iOS, Android and Apple Watch app prototypes.
React Proto - React application design and prototyping tool
Icons8 Lunacy - Free graphic design software with built-in resources. Fully compatible with Sketch and works offline
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.
Flinto - The prototyping tool designers have been waiting for.
Invision - Prototyping and collaboration for design teams