Microsoft isn't exactly known for releasing things early, but that's just what its done with the beta version of its new Hyper-V virtualization software, which is included as part of Windows Server 2008 RC1 Enterprise. As Microsoft itself points out, that was originally only expected to be released in the first quarter of 2008, but it says it decided to let things loose early in order to let customers evaluate the feature and provide feedback before the final release.
The software itself takes aim squarely at VMWare's territory, allowing users to configure an array of virtual machines and run multiple operating systems simultaneously. If betas aren't your thing, however, you can look for the final version to roll out "within 180 days" of the release of Windows Server 2008.