React Native - A framework for building native apps with React
Thunkable - Powerful but easy to use, drag-and-drop mobile app builder.
Flutter.dev - Build beautiful native apps in record time 🚀
BuildFire - BuildFire is the easiest way for small businesses to build a mobile app in a matter of minutes for iOS and Android.
Onsen UI - HTML5 Hybrid Mobile App UI Framework - work with Angular, React, Vue, Meteor & pure JavaScript. Material & Flat design.
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.