Is there a tool which can read Ruby code and visually (as GIF, PS, etc.)
present it? Like doxygen for C++.

I think this can be done without need to wrote parser because of great
Ruby's introspection facilities. With help of something like graphviz
www.research.att.com/sw/tools/graphviz

-- 
If you can't explain something to a six-year-old, you really don't
understand it yourself. 
		-- Albert Einstein