Invision - Prototyping and collaboration for design teams
Xamarin.Android - Integrated environment for building not only native Android but iOS and Windows apps too.
Moqups - The most stunning HTML5 app for creating resolution-independent SVG mockups, wireframes & interactive prototypes for your next project
Qt Creator - Qt Creator is a cross-platform C++, JavaScript and QML integrated development environment. It is the fastest, easiest and most fun experience a C++ developer could wish for.
Balsamiq - Balsamiq. Rapid, effective and fun wireframing software.
Rider - Rider is a cross-platform .NET IDE based on the IntelliJ platform and ReSharper.