Immediate Mode Graphical User Interface with minimal dependencies. [MIT]

Lightweight GUI toolkit for desktop and embedded. [GPL/Free/Proprietary] website

Simple and portable (but not inflexible) GUI library in C that uses the native GUI technologies of each platform it supports. [MIT]

A single-header ANSI C gui library. [PublicDomain]

Immediate Mode Plotting widgets for imgui. [MIT]

A library for creating native cross-platform GUI apps. [LGPLv2]

Lightweight, fine-grained, resolution independent, modular GUI library. [MIT]

Use any web browser as GUI, with your preferred language in the backend and HTML5 in the frontend. [MIT] website

The HTML/CSS User Interface library evolved. Fork of libRocket. [MIT]

GPU Accelerated C++ User Interface, with WYSIWYG developing tools, XML supports, built-in data binding and MVVM features. [Ms-PL]

Native, mobile, cross-platform GUI Framework. [GPL/LGPL/Proprietary] website

A minimalistic cross-platform widget library for OpenGL 3.x or higher. [BSD]

Cross-platform modern c++ GUI. [Zlib] website

Modern C++17/20 framework to create console (CLI), forms (GUI like WinForms) and tunit (unit tests like Microsoft Unit Testing Framework) applications on Windows, macOS, Linux, iOS and android. [MIT]

Fast, flexible and simple GUI. [MIT]

A modern, cross-platform C++ webview library. [MIT]

A library to create charts in wxWidgets applications. [MIT] website

Flexible, cross-platform GUI library.

Fast, light, cross-platform C++ GUI toolkit. [LGPL2]

an open-source, cross-platform widget toolkit. [LGPL]

A multi-platform toolkit for creating graphical user interfaces. [LGPL]

The official C++ interface for the popular GUI library GTK+. [LGPL]

Multi-platform toolkit for building graphical user interfaces. [MIT]

Nana is a cross-platform library for GUI programming in modern C++ style. [Boost]

Qt plotting widget without further dependencies. [GPLv3]

Qt Widgets for Technical Applications. [Own based on LGPL]

A feature-rich Qt/OpenGL-based C++ programming library, providing essentially a bunch of 3D-widgets. [zlib]

Sciter is an embeddable HTML/CSS/scripting engine aimed to be used as an UI layer of modern desktop applications. [Free/Commercial]

A C++ library that lets developers create applications for Windows, Mac OS X, Linux and other platforms with a single code base. [Own LGPL]