AppConvertly.com - AppConvertly - convert your website to Android & iOS app. No coding required. Easy solution to reach new audience in 5 minutes https://www.appconvertly.com/
Marvel - Turn sketches, mockups and designs into web, iPhone, iOS, Android and Apple Watch app prototypes.
Create - CREATE is a powerful and intuitive mobile creativity tool.
Invision - Prototyping and collaboration for design teams
Thunkable - Powerful but easy to use, drag-and-drop mobile app builder.
MIT App Inventor - App Inventor is a cloud-based tool, which means you can create apps for phones or tablets right in your web browser.