In March 2009 virtualization.info reported that Citrix was working on a hosted version of XenServer, dubbed XenWorkstation. Apparently, we were wrong (or Citrix decided to indefinitely postpone it, as some sources report).
What really happened, in April 2009, is that Xen.org announced the open source project Hosted Xen (HXEN): a type-2 (hosted) virtual machine monitor (VMM) that runs on 32bit versions of Windows (XP, Vista and 7) and Mac OS .
The HXEN code is a snapshot of the Xen code base used in XenServer and nothing stops Citrix from adding its own code and market the product as XenWorkstation.
One year after the announcement, HXEN still is in early beta, there’s not yet a version for 64bit OSes and not even a port for Linux, and Xen.org is calling for more developers.
This may mean two things: or there’s not enough interest around the project (possibly because of KVM and Oracle/Sun VirtualBox) or the Xen maintainers are increasing their commitment to get the platform more stable before Citrix finally jumps in.