Xen API Libs is a set of libraries and utilities in OCaml 3.12 that are used by xapi. The libraries are a component of the Xen Cloud Platform (XCP) project.
Xen Cloud Platform (XCP) is an open source enterprise-ready server virtualization and cloud computing platform. XCP builds on the Xen Hypervisor; and provides network and storage support, and management tools in a single, tested installable image.
XCP runs many guest operating systems, including Linux and Microsoft Windows.
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You can usually find the developers hanging out in #xen-api on freenode.