Thunkable - Powerful but easy to use, drag-and-drop mobile app builder.
Siberian CMS - Siberian is an Open-Source and Free App Maker. Unlimited Push Notifications. Unlimited features. Fully Customizable. Download it and build your own app now!
Xamarin.Android - Integrated environment for building not only native Android but iOS and Windows apps too.
Dropsource - Mobile development platform for building native iOS & Android apps
Kodular - Much more than a modern app creator without coding
GoodBarber - GoodBarber is a mobile app creation platform.