Puma
A Ruby/Rack web server built for concurrency
Unlike other Ruby Webservers, Puma was built for speed and parallelism. Puma is a small library that provides a very fast and concurrent HTTP 1.1 server for Ruby web applications. It is designed for running Rack apps only. What makes Puma so fast is the careful use of a Ragel extension to provide fast, accurate HTTP 1.1 protocol parsing. This makes the server scream without too many portability issues.