XAPI comes in several variants
XCP ISOs (this page)
The XCP ISO is available for download here. XCP - a subset of XenServer - installs onto your host from an ISO, providing a complete enterprise-ready out-of-the-box server virtualization and cloud computing platform after install.
Important Notice: Before June 2013, XenServer was not fully open sourced. For this reason, the Xen Project made XCP available for download from this page. Since XenServer is now fully open source, the Xen Project will not release versions of XCP after XCP 1.6. See our FAQ for more information. You can download a full open source version of XenServer from XenServer.org.