wxGlade is a GUI designer written in Python with the popular GUI toolkit wxPython which helps create wxWidgets/wxPython user interfaces. At the moment it can generate Python, C++, Lisp, Perl and XRC (wxWidgets' XML resources) code. It is not a full featured IDE, but simply a "designer": the generated code does nothing apart from displaying the created widgets.
While not related to Glade Interface Designer for GTK+, they are similar in idea and interface. As such they have comparable possibilities, and a user knowing one can quickly learn the other. Output files are not interchangeable (Glade using GladeXML, wxGlade XRC), however.