Puma
A Ruby/Rack web server built for concurrency
...If you are using Bundler, just add Puma to your project's Gemfile. Once you've installed your bundle, start Puma. If you are not using Bundler, you can install Puma directly from the command line. On MRI, there is a Global VM Lock (GVL) that ensures only one thread can run Ruby code at a time. But if you're doing a lot of blocking IO (such as HTTP calls to external APIs like Twitter), Puma still improves MRI's throughput by allowing IO waiting to be done in parallel.