Standards evolve in a lot of different ways. However, broadly speaking, they fall into two main buckets: de jure and de facto (to use the Latin-derived legalese). By law and by fact.
In high tech as elsewhere, it's often a matter of historical accident and political maneuvering that determines which approach wins out in a particular area of technology. And it can be a high-stakes game for the companies involved, with big players often seeking to position their approach as a "standard" even if it's only standard in the sense of being ubiquitous (think Microsoft Windows) while the smaller guys tend to favor approaches blessed by standards bodies or at least industry corsortia.
In cloud computing, we're seeing almost all the forms of standards-making coming into play with the primary goal of promoting interoperability among different cloud service providers and between private and public clouds.
On the de jure side, the most significant standards-making effort is taking place under the auspices of the Distributed Management Task Force (DMTF), an established organization in the management standards space. AMD, Cisco, Citrix, EMC, HP, IBM, Intel, Microsoft, Novell, Red Hat, Savvis, Sun Microsystems, and VMware announced in April 2009 (PDF) that they would comprise the board for an Open Cloud Standards Incubator within the DMTF.
If you were to observe that none of those companies currently have a big play in public cloud infrastructure, you would be correct. Microsoft has its Platform-as-a-Service Windows Azure play, and a number of those companies are very active in working with enterprises to build internal cloud-style IT, but none have an Infrastructure-as-a-Service (IaaS) offering in the vein of the conspicuously absent Amazon.
And it's Amazon Web Services (AWS) that has clearly emerged as the de facto standard for IaaS. The fact that Amazon is one of the first vendors that comes to mind in just about any discussion of public clouds is one indication. Another is the growing ecosystem of companies like RightScale that add additional features to AWS--not uniquely, but first and foremost. We now even have an open-source project and company, Eucalyptus, that lets organizations implement their own clouds that are compatible with many AWS services.
Now one of Amazon's competitors, Rackspace, is taking yet another approach to promoting its implementation as a standard. It's open-sourcing the specifications for its Cloud Servers and Cloud Files API under the Creative Commons 3.0 Attribution License. It also has made available its Cloud Files language bindings for Java, PHP, Python, C#, and Ruby under the MIT license.
The Creative Commons license that Rackspace is using lets users both share and change the work so long as they provide attribution to the creator, in this case Rackspace. The MIT license is a very permissive license in the vein of BSD that allows essentially any use of the code including its use within proprietary software.
Rackspace has emerged as a major player in public cloud infrastructure. Cloud Servers competes with Amazon EC2 and Cloud Files with S3. It also has a product called Cloud Sites, based in part on technology from its Mosso acquisition, that is more of a PaaS offering with dynamic scalability (but that's not part of this announcement).
This announcement doesn't fundamentally change the landscape. However, it does give an already well-established IaaS vendor a point of clear differentiation from its biggest competitor.