Entity GUI tool?

[icebear]

The ubuntu synaptic package manager claims:

        XML-based GUI builder for GTK+
        Entity is an XML-based GUI builder and application scripting framework.
        It combines the ease of use of XML for GUI layout and the power of Perl,
        Python, TCL, JavaScript, and C for the application logic.  An Entity GUI
        is usually much shorter than the same program written in any other
        language.

        This package contains the core portions of Entity along with Perl