First we should limit the number of toolkits to these, which are default avaible at every normal desktop linux distrybution.
Afaik there only 2, gtk+ ( NO GTKMM) and QT.
Ok then to qt
nice, but the license sucks.
LGPL, ok, but looks ugly and GUI programming in
Assembler is over.
Portability ? Nope, the win32 Port was a one man show.
OOP with C, RUNTIME typechecking lol ?.
Modules are nice but, in 99% of the cases, the modules aren`t installed on the default linux distribution.
And gtk is only a raw toolkit, not a Appframework.
And then u call this RAD ?
A gui designer doesnt count for me as the only thing u need for RAD.