from the README:

Xclasses is a C++ layout library for the X Window System.  The
sizes of all objects (gadgets) change with the size of the font
and the size of the window.

All gadgets have the same base class (class gadget) so they are
all used the same way.  Gadgets are put together in groups which
manage the sizes of the gadgets (or groups) inside.

WWW:  http://www.js-home.org/Xclasses/

Trevor Johnson