It's a pity that Fresco (http://fresco.org/) didn't proceed further. It
was an interesting concept. Server side had loadable widget toolkits and
clients used the toolkit over CORBA. Because the calls were high level
i.e. few, performance isn't an issue in this case (even over network). All
drawing was done using a scenegraph i.e. UI was fully transformable.
Y-windows (http://www.y-windows.org/) had later a similar "widgets on
server side" idea and I remember also another earlier attempt at this that
went a bit further than Y-windows (it was aimed more at embedded devices).