Excellent recommendation, I saw it come up on HackerNews, a while back. I think these micro web frameworks are a great way for developers to explore and experiment with coding concepts. I guess we should also mention the Ruby Sinatra project: https://github.com/sinatra/sinatra
You should also check out TinkerPop (http://www.tinkerpop.com/) -- another exceptional developer group. Graphs are a much more elegant way of storing relational data, and TinkerPop has developed the open-source software stack for the emerging world of graph databases.