Passenger-Stack: Quickly Install a full Ruby and Passenger Stack
Passenger-Stack is a set of scripts for the provisioning tool Sprinkle that make installing a full Ruby, Apache and Passenger-based stack almost a one-line task. It'll take almost any UNIX-y (correction: Ubuntu / Debian) server of your choice from a generic install through to deploying Rack-based apps (including those built with Rails, Merb, Sinatra, and Ramaze).
The Sprinkle scripts behind Passenger-Stack were developed by Ben Schwarz and the best introduction is his five minute screencast showing how it works (on Ubuntu 8.10 hosted with Slicehost). Ben is very keen for people to fork the scripts on Github and customize them further.
If you're not familiar with Sprinkle, by the way, it's a "software provisioning tool" that you can use to perform installs and remote builds with. In essence, it allows you to write installation scripts using a Ruby-based DSL.