Rails, still?
"Sinatra is Ruby with Rails in mind. You will find yourself using more of Rails in your Sinatra application over time and ask yourself why you're not just using Rails."<p>This is an important point. If you've ever developed a non-trivial application using Sinatra, Express or any other "micro" or "non-opinionated" framework, you'll have hit this wall quickly.<p>To riff on Greenspun's Tenth Rule, "Any sufficiently complicated $MICRO-FRAMEWORK application contains an ad hoc informally-specified bug-ridden slow implementation of half of Ruby on Rails."