VMware has launched the first release candidate (RC1) of its Fusion virtualization software that lets Mac owners run Windows on Intel-based machines, one of the last steps toward finalizing its rival to Apple's own Boot Camp and Parallels' flagship virtual machine, Parallels.

Fusion RC1, which can be downloaded free of charge from the VMware site, is "feature complete," said VMware. Among the changes since Beta 4, which was released last month, are "Unity" support for Windows Vista, Windows Server 2003 and the 64-bit edition of Windows XP. Unity lets users run Windows applications directly from the Mac desktop, without actually launching into a Windows virtual machine (VM); the previous version of Fusion only offered Unity support for Windows XP.

VMware also cited RC1 improvements to Boot Camp VM performance, faster resume from the Mac's suspend state, numerous bug fixes and "experimental" support for the developer's edition of Mac OS X 10.5, 'Leopard' released by Apple at last month's Worldwide Developers Conference.

Fusion is on track for a final release next month, said VMware. Until then, it will continue to sell the VM software at the preorder price of $39.99; when the product ships, it will retail for $79.99.

VMware's competitors include Apple, which currently gives away the dual-boot utility Boot Camp and plans to integrate it in Mac OS X 10.5 Leopard, due to ship in October; and Parallels Desktop for Mac, Apple-sanctioned VM software that shipped in Version 3.0 several weeks ago.