KWWidgets: Multi Platform GUI Toolkit
KWWidgets is a free, cross-platform and open-license GUI Toolkit with Python bindings. In addition to common UI widgets, KWWidgets interfaces to visualization libraries like VTK and offers high-level visualization-oriented widgets like surface material editors, simple animation generators, transfer function editors, annotation editors, window/level and volume property preset editors, text property editors, 2D and 3D rendering widgets, etc.
http://www.kwwidgets.org/Wiki/KWWidgets