Most programs proposed here are licensed under AGPL, and available for GNU/Linux (and other POSIX-compliant OSes), OS X and Windows, natively on IA-32, AMD64 and ARM (both AArch32 and AArch64) compatible architectures.
The Atlas toolkit: lightweight and easy to use library for developing versatile graphical interfaces. Here's the preview of the application from the TodoMVC project made with the Atlas toolkit:
Some programs :
XPPq : an XML preprocessor ; transforms an XML file following included dedicated directives related to file inclusion, macro definition/expansion, variable setting/testing…,
CLI tools : section dedicated to the tools (programs with a command-line interface, not tied to an application) based on the Epeios framework,
GUI apps : section dedicated to applications (software with a graphical user interface) based on the Epeios framework.