Qt
GTK
Xamarin
WompMobile
wxWidgets
OutSystems
Oracle Mobile Application
Mendix
DroidScript
Appcelerator Titanium
NativeScript
B4X
Apache Cordova
React Native
Sencha Touch
jQuery Mobile
DroidScriptGTK - GTK+ is a multi-platform toolkit for creating graphical user interfaces.
Appcelerator Titanium - Appcelerator Open Source
Xamarin - Create iOS, Android and Mac apps in C#
NativeScript - Build truly native apps with JavaScript
WompMobile - WompMobile offers tow kind of functions โ first creating new mobile apps and secondly converting the websites into mobile applications.
B4X - Cross platform development tools for native iOS, Android, desktop and server applications.