From their site: "EUCALYPTUS -- Elastic Utility Computing Architecture for Linking Your Programs To Useful Systems -- is an open-source software infrastructure for implementing Elastic/Utility/Cloud computing using computing clusters and/or workstation farms.".
Not only is it "interface-compatible with Amazon.com's EC2" but it is also "designed to be modified and extended so that multiple client-side interfaces can be supported"
Now, that is good news. If you happen to be an ISP starting to get nervous of this new world of large utility computing providers, then group together, get involved with EUCALYPTUS and create a marketplace.
EUCALYPTUS would appear to be, a full blown, open sourced standard at the "Hardware as a Service" level of the computing stack. All we need now are multiple providers, some trademarks and a compliance authority.