From the Xen blog:
Citrix Project Satori is the result of a collaborative agreement between XenSource and Microsoft, and was carried forward after XenSource was acquired by Citrix Systems. The base Satori components are released by Microsoft as the Linux Integration Components for Hyper-V, and provide support for paravirtualized XenLinux guests running on Hyper-V. The Linux Integration Components can be downloaded here.
The complete source code and license information (GPL version 2) on this project is now available here.