Ask HN: What is the most *fun* web development stack?

When I started with Ruby on Rails back in 2006, it was because I was running away from Java and I thought that it was the most fun stack out there. I think I chose wisely and I really enjoyed (and still enjoy) my time with Ruby and Rails.

If you are using a web stack that you think might be one of the most enjoyable and fun, what is it?