sinatra-flash

https://github.com/SFEley/sinatra-flash

A Sinatra extension for setting and showing Rails-like flash messages. This extension improves on the Rack::Flash gem by being simpler to use, providing a full range of hash operations (including iterating through various flash keys, testing the size of the hash, etc.), and offering a 'styled_flash' view helper to render the entire flash hash with sensible CSS classes. The downside is reduced flexibility -- these methods will *only* work in Sinatra.