Wikipedia
WxFormBuilder
wxFormBuilder is an open source GUI designer application for wxWidgets toolkit, which allows creating cross-platform applications. A streamlined, easy to use interface enables faster development and easier maintenance of software. It is written in C++.
wxFormBuilder is a visual development tool, but also allows including non-graphical components. It can emit C++, Python, PHP, Lua and XRC code. Emitted code cannot be edited directly in the program.