When developing cross-platform applications we have a basic decision to make: use a wrapper like wxWidgets (C/C++) or Lazarus/LCL (Pascal) or use a GUI toolkit like FLTK (C/C++) or fpGUI (Pascal). The wrapper relies in the underlying API of the host desktop environment (Win32, Mac OS X, GTK+, X11, Motif, etc) in order to draw its widgets; the toolkit draws the widgets by itself, emulating the native GUI.
There is a very interesting thread about this topic on Lazarus mailing list.
