IUP

IUP is a cross-platform graphical user interface (GUI) toolkit designed for building applications in C and other languages. It provides a portable API capable of creating windows, dialogs, menus, buttons, input fields, canvases, and many other controls, with the goal of delivering native-looking interfaces on multiple operating systems. IUP emphasizes a straightforward programming model and easy integration with existing codebases.

The toolkit was developed by the Tecgraf research group at the Pontifical Catholic University of Rio Grande do Sul (PUCRS) in Brazil. Since its inception in the 1990s, IUP has been maintained and expanded by its developers and a user community. It runs on Windows, macOS, and Unix-like systems, often using native widgets where available and falling back to its own rendering when necessary. In addition to core widgets such as labels, buttons, text fields, toggles, lists, trees, and tabs, IUP includes support for dialog creation, menus, and OpenGL rendering through an IupGL module.

IUP is primarily written in C, but bindings exist for other programming languages, notably Lua and Python, enabling developers to create GUIs with scripting languages in addition to or instead of C. The project distributes documentation, example programs, and a self-contained toolchain to build and deploy applications. IUP is released under a permissive license to encourage broad adoption in open-source and commercial projects.