Psystar, the Florida-based systems integrator that defied Apple's no-cloning rule by selling Mac desktop knockoffs, has introduced rack-mount servers that can run the Leopard Server operating system, an apparent challenge to Apple's Xserve system.

The OpenServ 1100, listed as a 1U server, and the OpenServ 2400, a 2U system, were launched this week. Both are "compatible" with several server operating systems, including Windows Server 2003 and 2008, Ubuntu Server, CentOS, and Mac OS X Leopard Server, the company said.

Psystar launched its Open Computer Mac clone about two months ago for $399, and then introduced soon after a beefed up version called OpenPro that ships with a choice of operating systems, including Ubuntu Linux, Windows Vista, Windows XP, or Apple's Leopard, which is also known as Mac OS X 10.5. The system is priced at $805, while a similarly configured Apple-branded computer would cost more than $2,000.

So far, Apple has made no public comments on Psystar selling systems in defiance of the company's policy against cloning. Apple's Leopard license agreement forbids third-party installations and sales.

Nevertheless, Psystar has been very vocal in marketing its products, claiming the systems cost a quarter of Apple's. The company also says Apple marks up the cost of its hardware by as much as 80%.

The latest Psystar systems are available with up to two Intel Xeon quad-core processors and have dual gigabit Ethernet and up to 16GB of memory. The 1100 model has up to 4 TB of storage, and the 2400 system up to 6 TB. Pricing starts at $1,599 and $1,999, respectively.

Psystar last month upgraded its line of Mac clones with an improved metal chassis, claiming the new V2 box is "virtually silent." The company also said it is ramping up its production capabilities and would offer an order-to-build time of just four days. Psystar also offers support for its systems.