From the Cloudiness, Chance of Openness dept.:
OpenStack is an open-source cloud platform designed to foster the emergence of technology standards and cloud interoperability. The initial components being offered through this project include the code that powers our Cloud Files (available today) and Cloud Servers (expected available late 2010). Leaders in the technology industry and other stakeholders support the project and are expected to help us drive a deployable, completely open cloud solution.

What does an open cloud mean for you?
Prevents vendor lock-in
Increases flexibility in deployment for a highly elastic commodity cloud
Offers a bigger, more robust ecosystem for more tools, better capabilities and a stronger platform
Gives you the freedom to decide how you want your cloud
Drives greater industry standards
Increases the speed of innovation in cloud technologies

rackspace.com