Lara

Lara Web Engine is a C# Web UI framework supporting web component development and reactive programming. - integrativesoft/lara

B4X

Cross platform development tools for native iOS, Android, desktop and server applications.

DiffMerge is a graphical file comparison program for Windows, Mac OS X and Unix, published by…

Build cross platform desktop apps with web technologies

Fast Light Toolkit - Fast Light Toolkit (FLTK)

FastAPI is an Open Source, modern, fast (high-performance), web framework for building APIs with Python 3.6+ based on standard Python type hints.

Build beautiful native apps in record time í ½íº

GTK+ is a multi-platform toolkit for creating graphical user interfaces.

JUCE is a wide-ranging C++ class library for building rich cross-platform applications and plugins…

JavaFX is the next step in the evolution of Java as a rich client platform.

MonoDevelop enables developers to write desktop and web applications on Linux, Windows and Mac OS X.

Nana C++ Library - a modern C++ GUI library

Polymer is a library that uses the latest web technologies to let you create custom HTML elements.

Qt for Python - Qt Wiki

C++

SPA front-end on steroids.

wxWidgets: Cross-Platform GUI Library