VMware vSphere (as known as VI in earlier versions) SDK includes a comprehensive set of APIs managing the vSphere CloudOS. It can be used to build different types of applications: standalone GUI applications, vSphere Client plug-in, utility tools, Web applications, server applications. It is becoming increasingly important as more and more enterprises become 100% virtualized with vSphere.
My company has created products like vSearch ("Super vCenter"), vijavaNG APIs, EAM APIs, ICE tool. We also help clients with virtualization and cloud computing on customized development, training. Should you, or someone you know, need these products and services, please feel free to contact me: steve __AT__ doublecloud.org.
Me: Steve Jin, VMware vExpert who authored the VMware VI and vSphere SDK by Prentice Hall, and created the de factor open source vSphere Java API while working at VMware engineering. Companies like Cisco, EMC, NetApp, HP, Dell, VMware, are among the users of the API and other tools I developed for their products, internal IT orchestration, and test automation.