Just a note about Tk -- it has built-in *bindings* in ruby, not a
built-in toolkit. You still need the Tcl/Tk backend, which must be
installed seperately on windows or *nix or mac. Not to mention that
Tile must be installed seperately (for the tk 1.8 stable branch at
least). Unless I've missed something, the only thing built-in about Tk
is the bindings, not the toolkit itself.

Regards,
Jordan