Thunkable - Powerful but easy to use, drag-and-drop mobile app builder.
Vuetify - Material Component Framework for VueJS 2
BuildFire - BuildFire is the easiest way for small businesses to build a mobile app in a matter of minutes for iOS and Android.
Buefy - Lightweight UI components for Vue.js based on Bulma
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.
Mint UI - Beautiful, reliable component library for Mint