Clive Crous on rupov:

rupov is still a baby, meaning, i only started work on it very recently
and it's never had any releases.  anything that is currently online (
http://www.darkarts.co.za/projects/rupov ) can be considered unstable
and
the api or even the design may be scrapped at any minute if i think it
can
be done better another way.

Povray is very easy, I would also recommend you have a look at it.  If
you
use a unix operating system (or a unix clone like linux etc) then look
at
"kpovmodeller" it's great ;)

rupov will be designed as an interface to povray, which is a raytracing
engine.  rupov will be usefull for creating rendered scenes that are
non-interactive.  For example I am using it to generate povray scenes
for
tiles in an isometric game I am making.  rupov generates the graphics
at
'compile time' which are then just drawn ingame.

Clive Crous on opengl

If you want to learn graphic programming, in the sense that you would
like
to create interactive scenes that respond to user interaction, then
opengl
is the way to go, and for ruby I reccommend 'rubygame':
   http://rubygame.seul.org/

It is also a new project, the latest online version "1.0" does not
include
  OpenGL, but the OpenGL code is already completed by the author and is
available through his repository.  He has said on his mailing list that
it
will be released any day now, for which I am waiting with much
anticipation :D

-- 
Clive Crous