Virtualization, as the buzzword du jour, gets applied in many unexpected ways. One use that may become more familiar is application virtualization, as VMware is snapping up Thinstall, a leading provider of the technology. The acquisition isn't a huge surprise, as VMware's two main competitors do app virtualization already. But it demonstrates that VMware takes the desktop market seriously.

Rather than let multiple operating systems run on the same computer, app virtualization seeks to give each application its own protected environment in which to run. For Windows, that means a virtual copy of the registry and other custom settings and Dynamic Link Libraries. The technology lets noncompatible apps share a system (say .Net 1.0 and .Net 2.0 apps); it also protects the host from the application and the app from the host.

Thinstall's main innovation has been to operate without the need of a client-side agent, or the need to load virtualized apps from servers. Competing products from Citrix Systems, Endeavors Technologies, Microsoft, and Symantec via its Altiris acquisition use agents and servers to monitor licensing and ensure that clients use the latest version of a virtualized app. All vendors bundle applications, registries, and other required components into a single executable file. That makes distribution easy, as it turns Windows applications into the desktop equivalent of virtual appliances, able to run with no installation procedure. That prospect appeals to both internal IT organizations and software-as-a-service vendors that require client-side software.

The downside of Thinstall's approach can be more complicated management, as there's no built-in way to see who is using which applications or whether they're patched. Thinstall gets around that shortcoming by partnering with network management vendors, notably LANDesk, which resells the Thinstall product and has integrated it into its own management software. LANDesk says its OEM agreement isn't affected by the acquisition, but with VMware also using virtualization management as its main differentiator in the hypervisor market, some tension seems likely.

NO STREAMING REQUIRED

At one point, Thinstall's serverless model was unique, with other vendors requiring that apps be "streamed" from servers at execution. Microsoft and Symantec no longer maintain this requirement. In November, Microsoft upgraded its streaming product to allow what it calls standalone delivery, which accomplishes much the same as Thinstall. It also renamed the software Microsoft Application Virtualization to emphasize that it can be used in nonstreaming architectures.

The other big competitor is Citrix, which developed a streaming system in-house, viewing it as the next generation of thin client technology. Streaming essentially does for thin clients what Ajax does for the Web--that is, it takes advantage of client-side processing and storage.

Other competitors include RingCube, a startup that applies virtualization per user rather than per application. Instead of giving each app a dedicated VM, RingCube creates a single virtual machine that's shared by all the user's applications and data. The shared VM ought to result in better performance when more than one app needs to be virtualized, but unlike Thinstall, RingCube doesn't help resolve application conflicts. RingCube originally aimed its technology at home users as the MojoPac, a USB drive that could hold a user's entire desktop. It has since moved into the enterprise.

But the real dark horse could be Google. In May it bought GreenBorder, an app virtualization startup focused on security. GreenBorder's technology is similar to RingCube's in that all virtualized apps share a single VM, but it was aimed at isolating untrusted downloaded applications. Google discontinued the products for new customers and hasn't said what it plans to do with the technology.