Thunkable - Powerful but easy to use, drag-and-drop mobile app builder.
Apache Cordova - Platform for building native mobile applications using HTML, CSS and JavaScript
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.
React Native - A framework for building native apps with React
Fuse - Fuse is a UX tool suite for mobile app designers and developers.
PhoneGap - Easily create apps using the web technologies you know and love: HTML, CSS, and JavaScript.