WxWidgets

wxWidgets lets developers create applications for Win32, Mac OS X, GTK+, X11, Motif, WinCE, and more using one codebase. It can be used from languages such as C++, Python, Perl, and C#/.NET.

The wxWidgets library is implemented in C++, with bindings available for many commonly used programming languages, among them, Python (wxPython), Erlang (wxErlang), Haskell (wxHaskell), Lua (wxLua), Perl (wxPerl), Ruby (wxRuby), Smalltalk (wxSqueak), Java (wx4j) and even JavaScript (wxJavaScript).