JUCE is an open-source cross-platform C++ application framework
A text-based widget toolkit
A modern, C++-native, test framework for unit-tests, TDD and BDD
Open source framework simplifying the creation of C++ applications
Static reflection for enums (to string, from string, iteration)
SDL library for Android, including several games.
Real-Time Event Frameworks based on active objects & state machines
Individual-based forward-time genetics simulation software
A multimedia framework based on Qt and FFmpeg
Object oriented frameworks - PowerBuilder, PowerServer & InfoMaker!
C++ application framework
MuldeR's Utilities for Qt
A simple 3D framework in C++
Software libraries for effective development of desktop applications.
C++ Frontend for the RenderMan Interface
C++ Statistical ToolKit
Development framework based on message driven provided
Cross-platform C++ library for use as a default application framework.
C++ Library for the Common Image Generator Interface
Source code is here - https://sourceforge.net/projects/lcmd-git/
High performance C++ library for building Wayland compositors