What is VMWare?

From the "About Us" page of the VMWare company website:

VMware was founded in 1998 to bring virtual machine technology to industry-standard computers. VMware delivered its first product, VMware Workstation, in 1999 and entered the server market in 2001. . .

More than 4 million users and over 20,000 corporate customers of all types and sizes use VMware software, including 99 of the Fortune 100 companies. Deploying VMware software to meet complex business challenges such as resource utilization and availability, customers have realized significant benefits, including lower total cost of ownership, higher return on investment and improved service levels to their customers.

VMWare is widely regarded to be the leader in the virtualization marketplace, and many corporate users are no doubt excited to have the company developing a virtualization solution for MacOS X.

What is a "Virtual Appliance"?

In the Virtual Appliance Marketplace, VMWare states that:

A virtual appliance is a pre-built, pre-configured and ready-to-run software application packaged with the operating system inside a virtual machine.

In non-technical terms, VMWare allows a company or programmer to configure a software program and an operating system for use and "wrap" them together as a "virtual appliance" so that no installation, setup, or configuration is required for the end user (beyond the installation and configuration of VMWare).

Virtual appliances can be particularly useful for legacy applications that may have been designed for an operating system no longer in widespread use or one that is not compatible with the underlying hardware.

Is there a way to use or convert a VMWare Virtual Appliance to run under Parallels Desktop for Mac?

Not officially, but as first spotted by TUAW, the Virtualization Daily website has written an excellent tutorial as a starting point for those interested in attempting to convert a VMWare Virtual Appliance to run under Parallels Desktop for Mac. Some virtual appliances are easy to convert and others are more challenging. Parallels also has a wide variety of their own Virtual Appliances.

Starting with version 3, Parallels also offers Transporter to "migrate your Windows PC, VMWare, or Virtual PC Virtual Machines to Parallels Virtual Machines". VMWare, likewise, offers an Importer that "makes it easy to convert your existing Parallels Desktop or Virtual PC 7.0 for Mac virtual machines to run with VMware Fusion".