Hoping to stay a step ahead of rival VMware, Citrix Systems is now shipping its XenDesktop product line of desktop virtualisation software.

Announced at the company's annual Citrix Synergy conference in Houston on Tuesday, XenDesktop comes in five editions, including a free bare-bones Express Edition that will give small businesses and developers a chance to test the product for as many as 10 users without having to worry about licensing fees.

XenDesktop delivers the Windows desktop to clients over the network, using virtual machine technology. These virtualised desktops are actually run on a central server, making it easier for them to be managed by IT staff.

After having a virtual monopoly on remote Windows desktop connection software, Citrix has been feeling some competitive heat lately from VMware.

Recently, smaller players such as MokaFive launched its MokaFive Virtual Desktop Solution, and earlier this month Qumranet, the start-up behind the increasingly popular KVM kernel-level virtualisation technology, also threw its hat into the desktop virtualisation ring.

Analysts say VMware's Virtual Desktop Infrastructure is still a year or two away from providing stiff competition to Citrix, but the virtualisation software vendor, which is majority-owned by EMC, clearly has Citrix's attention.

In October of last year, Citrix spent $500 million to acquire VMware competitor XenSource. XenDesktop uses Xen's hypervisor software, and Citrix has a datacentre product called XenServer that is based on XenSource's product.

Although XenDesktop takes a different approach from Citrix's older XenApp software (formerly known as Presentation Manager), it is a similar type of product. With XenApp, users are delivered applications, or even very basic Windows environments called published desktops, from a central server.

Published desktops are generic and cannot be easily customised for individual users. In contrast, XenDesktop gives the users a full-featured Windows environment, but one that can still be centrally managed by IT staff.

This will make XenDesktop appealing to many more desktop users in the enterprise, said David Roussain, Citrix's corporate vice president of virtualisation marketing.