A very easy to use GUI C++ framework for Windows and *NIX systems. Supports WIN32 API on Windows platforms, and Athena and Motif X widgets on *NIX systems. First developed in 1995, is still in active development. Currently working on Version 2.0.
The V GUI application graphical interface model is a compromise between everything that was used at the time of its inception, including its prediction of a number of other simplified approaches. It takes both the layered approach of Athena widgets and the seemingly random and chaotic Win32 functions and translates them into the common language of a generic application model with only the most essential decorations and controls. At the surface level, V forms a strictly object-oriented model that can be manipulated easily by students to form relatively complex applications, while it descends into the dirty details of whatever interface it translates, making it a good candidate for more robust applications for sophisticated programmers. Since the language derived from the V model is something of a trade-based pidgin, it can remove much of the pain of creating parallel structures in disparate environments. My experience is limited to the Win32-to/from-Linux (mostly Red Hat distros), but if Bruce Wampler's approach could be extended into newer developments such as privileged memory models and STL structure and algorithm support, any C++ platform could become practically polyglot in its graphical interface.