Google App Engine - A powerful platform to build web and mobile apps that scale automatically.
Heroku - Agile deployment platform for Ruby, Node.js, Clojure, Java, Python, and Scala. Setup takes only minutes and deploys are instant through git. Leave tedious server maintenance to Heroku and focus on your code.
Pivotal - Pivotal Software provides enterprise PaaS-based solutions.
OpenShift - OpenShift gives you all the tools you need to develop, host and scale your apps in the public or private cloud. Get started today.
Cloudify - Accelerating Software Development & Deployment
DigitalOcean - Simplifying cloud hosting. Deploy an SSD cloud server in 55 seconds.