Puma: A Ruby Web Server Built For Concurrency

Puma is a simple, fast, and highly concurrent HTTP 1.1 server for Ruby web
applications.  It can be used with any application that supports Rack, and is
considered the replacement for Webrick and Mongrel.  It was designed to be the
go-to server for Rubinius, but also works well with JRuby and MRI.  Puma is
intended for use in both development and production environments.

Homepage:
http://puma.io/
