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.
BuildFire - BuildFire is the easiest way for small businesses to build a mobile app in a matter of minutes for iOS and Android.
Bubble.io - Building tech is slow and expensive. Bubble is the most powerful no-code platform for creating digital products.
Android Studio - Android development environment based on IntelliJ IDEA
Xamarin.Android - Integrated environment for building not only native Android but iOS and Windows apps too.