Thin

Thin is a Ruby web server that glues together 3 of the best Ruby libraries in web history:

• the Mongrel parser, the root of Mongrel speed and security
• Event Machine, a network I/O library with extremely high scalability, performance and stability
• Rack, a minimal interface between webservers and Ruby frameworks

Which makes it, with all humility, the most secure, stable, fast and extensible Ruby web server bundled in an easy to use gem for your own pleasure.