Sinatra's sweet spot is in light weight apps and services. It's simpler than Rails and gives you more help than pure Rack when you want to prototype a feature,

Sinatra's sweet spot is in light weight apps and services. It's simpler than Rails and gives you more help than pure Rack when you want to prototype a feature, or build services for a SOA based application. See http://neovigator.heroku.com http://neovigator.heroku.com for an example sinatra app.