There are hundreds of short Ruby programming puzzles that you do
interactively on the site. You get scored on your solutions and the
problems are labelled for difficulty and type.
Although there are a lot of puzzles, it needs more! so please submit one
if you have the time.
I find doing these short simple puzzles very helpful for retention.
Only thing I want for Rubeque is a rating system - some of the problems
are a bit trivial, but some are quite good, like the FizzBuzz one, which
opened my mind a bit.