Dedoimedo posted a short review of OpenXenManager, a standalone, free clone of XenCenter for managing XenServer and Xen Cloud Platform (XCP) from non-Windows systems
OpenXenManager is a free clone of the XenCenter and is supposed to be fully compatible with both XenServer and the freeware XCP. The program comes bundled as a bunch of Python scripts, contained in a single archive, so the deployment is a breeze pretty much everywhere. You won't get any visual integration with your desktop theme, though.OpenXenManager alternative to XenCenter
You might want to consider this program if you're going for an all-free combo setup with XCP perhaps, or if you require GUI management from Linux, as OpenXenManager does run on non-Windows machine, unlike XenCenter, which is for Windows only. Now, the official page looks a little out of date, so you might want to take long-term support into consideration, too. But enough talking, let's OpenXenManager in action.