Deployment

Ansible (Documentation) (Github)

Configuration management with Ansible

vagrant-ansible

Multi Server Flask Application Development Environment with Vagrant and Ansible, Gihub
BOSH

Dr Nic's Getting Started with BOSH has never been easier
Capistrano
Mina (Github)

mina-sidekiq
Sprinkle is a software provisioning tool you can use to build remote servers with. eg. to install a Rails, or Sinatra stack on a brand new slice directly after its been created

Collection of recipes for various Ruby on Rails deployment setups
Ironfan

Cloud

IaaS and PaaS also available as local clouds

VMware Cloud Foundry
Gigaspaces Cloudify
Apache CloudStack
DevStack is a documented shell script to build complete OpenStack development environments
JoyentCloud is build on SmartDataCenter
Red Hat OpenShift is available as OpenShift Origin LiveCD

Virtualization as local clouds

AWS EC2

Fog, (Github) is the Ruby cloud computing library.
Judo
Sumo, Sumo: One-off EC2 Instance Launching
MongoDB on EC2 and EBS

PoolParty.rb

PoolParty.rb uses Chef to deploy to Amazon's EC2 cloud service and supports auto-scaling.

Rubber

Rubber is a Capistrano plug-in to deploy to Amazon's EC2 cloud service, to Digital Ocean, to SSH-accessible dedicated hosts and to Vagrant.

AWS Elastic Beanstalk

Virtual Machines

Vagrant

Vagrant uses Chef or Puppet to deploy to virtual machines using VirtualBox.

Vagrant
Vagrant boxes
Creating a Local Riak Cluster with Vagrant and Chef
Making CI easier to do than not to with Hudson CI and Vagrant
Testing Rails for the masses!
Vagrant VBox for Jenkins
Using Vagrant with the Opscode Platform
vagrant-joyent, vagrant-smartos
VeeWee eases the building of Vagrant boxes