Last week VMware finally made good on its promise at Apple's Worldwide Developer Conference (WWDC), releasing a public beta version (registration required) of its new virtualization software for Mac OS X, code-named Fusion. Like Parallels Desktop and Q, Fusion enables anyone with an Intel Mac to run Windows, Linux, or most other PC operating systems within Mac OS X; unlike Boot Camp, these solutions require no rebooting.

Because Parallels Desktop is so highly regarded and has become an early hit, Fusion seemingly has an uphill battle for market share. But the program is certainly on the right track. This beta release offers full support for most USB 2.0 devices; even the latest beta version of Parallels Desktop, which has preliminary USB 2.0 support, doesn't yet work with isochronous devices like video cameras. (Isochronous means "happening at regular intervals." Isochronous devices don't buffer their information but need the operating system to accept what they send when they send it.)

Fusion supports drag-and-drop between Windows and Mac OS X, a feature added to Parallels Desktop only a couple of weeks ago in a recent beta. And Fusion enables users to specify how many processor cores should be allocated to virtual machines; in Parallels, only one core is used at present. Early reports from beta testers indicate that Fusion's performance is excellent, in some cases exceeding that of Parallels.

On the other hand, Fusion currently has nothing to compare to Coherence, the new Parallels feature that effectively lets Windows applications run independently alongside Mac OS X applications, rather than being constrained to a separate Windows window. And the initial beta of Fusion cannot read Boot Camp volumes (as the latest Parallels betas can), forcing Boot Camp users to install a separate version of Windows.

VMware has not announced the final name, pricing, or release date for Fusion, but they're clearly aiming to give Parallels a run for their money. The inevitable competition will be interesting to watch.