Written in C, can be used in both C and C++.
Available On most UNIX and other platforms with XLib installed, meaning
NT and PowerPC.
Has Forms designer, which will interactively generate C code to create
forms user specifies.
Can create custom forms.
Doesn't look as sleek as the other two.
Doesn't support Multithreading
Has GUI Builder
Boxes & Frames:
Scrollbars, Counters, Sliders & Dials:
Input Fields, Pop up messages & Menus:
Tabs and other Miscellaneous things: