Sinatra is a free and open source software web application library and domain-specific language[2] written in Ruby.

Instead, Sinatra focuses on "quickly creating web-applications in Ruby with minimal effort.

[5] Some notable companies and institutions that use Sinatra include Apple,[6] BBC,[7] the British Government's Government Digital Service,[8] LinkedIn,[9] the National Security Agency,[10] Engine Yard, Heroku, GitHub,[11] Stripe, and Songbird.

It inspired multiple ports and similar projects in other programming languages, such as Express.js and Scalatra.

[5][13] Mizerany and Heroku's Adam Wiggins introduced and discussed Sinatra at RubyConf 2008.