DirectFB is a thin library that provides developers with hardware graphics acceleration, input device handling and abstraction, an integrated windowing system with support for translucent windows and multiple display layers on top of the Linux framebuffer device. It is a complete hardware abstraction layer with software fallbacks for every graphics operation that is not supported by the underlying hardware.
Wt is a C++ library for developing Web applications with an API that is widget-centric and inspired by existing C++ graphical user interface APIs. To the developer, it offers abstraction of Web-specific implementation details, increasing the accessibility and portability. Under the hood, the library uses the latest techniques (HTML5, Ajax, WebSockets) to handle user events and update the Web page.
The Ecere SDK is a cross-platform toolkit for building software applications. It currently runs on Windows, Linux, Mac OS X (through X11), FreeBSD, and the Android OS. It should run on other Unix platforms with minor testing/tweaking. With the Ecere SDK, you can develop applications once and deploy them on all supported platforms alongside a lightweight runtime environment. It introduces eC, an object oriented language derived from and fully compatible with C, compromising neither runtime performance nor ease of use. A built-in 3D engine supporting both Direct3D and OpenGL is fully integrated.
Bambookit GUI is a completely XML-scriptable user interface to build real-time interactive Web application front-ends. Applications occupy 100 Kb of device memory and run on any Java-enabled browser. Users can move windows, resize containers, scroll and sort tables, lists, trees, see real-time data display, use a layout manager, and more. All rendering and event handling is managed in the XML scripts.
Panwa is a framework based on the Qt toolkit for writing platform independent applications with high quality graphical user interfaces. Panwa applications are meant as a complementary approach to Web applications, and the framework makes it possible to create applications that combine the flexibility of Web applications with the usability advantages of native applications. Therefore, you can see it as an implementation of a "rich thin client".
libTISCH is a framework for easy development of multi-touch applications. It contains tools for video processing, calibration, gesture recognition and, most importantly, a GUI toolkit with widgets that utilize the multi-touch gestures detected by the lower layers. It runs on Linux, Mac OS X, and Windows.