Phusion Passenger is an Apache module that allows you to run Ruby on Rails applications from within Apache. It promises a minimal configuration experience beyond uploading your application files. I have not played around with it yet myself, but it looks interesting:
The name of the project seems to have gone through a few iterations, hence the modrails.com domain above. Previously it was known as mod_rails and mod_rack.
When I last looked seriously at Ruby on Rails, Mongrel was the web server of choice but it would appear that Phusion Passenger has more traction now, especially for production environments. I found a good overview of the benefits of using Phusion Passenger versus Mongrel here: