rBuilder is the innovative platform offered by rPath able to simplify and partially automate creation of Linux-based appliances.
Since ever rBuilder supports (live and installable) ISOs and VMware .vmdk output formats, becoming one of the preferred solution to develop new virtual appliances. But if you are not using VMware products you had to convert these images in a more flexible format, with a so-called virtual to virtual (V2V) migration.
Now rBuilder allows users to save their distros in raw hard disk image format, permitting to use them in other virtualization platforms like Xen, Parallels or QEMU.
And, not being enoug, rPath is now extending support to Microsoft .vhd format, allowing everybody to create virtual appliances for current Virtual Server 2005 R2 and upcoming Windows Server Virtualization.