Phusion Passenger is an application server, designed to be fast, robust and lightweight. By combining Heroku with Phusion Passenger, you can boost the performance of your apps, utilize the available resources on your dynos much more efficiently and increase its stability. Phusion Passenger for Heroku brings the power of Nginx to your dynos. Nginx is an extremely fast and lightweight web server that powers 10% of the Internet. All the cool guys are rapidly switching to Nginx. Phusion Passenger replaces Thin and Unicorn, and makes full use of Nginx to serve your Ruby apps faster and better.