I am currently developing a simple OpenGL-like screen multiplexer for Xen Virtual Machines. For more info on my other Xen-related projects, see my home page.
The HG repository with the actual code is here. Some assembly is required.
The first shot shows the Linux kernel frame buffer mapped onto an OpenGL texture. Everything is handled from with the VM -- e.g. the program in the VM could decide to map the console onto a cube or something similar.
The second shot is taken on my IBM Thinkpad T42p, and shows 3 Xen VM's displaying their OpenGL content on a shared display, managed by a user-level server in dom0. All Windows update their contents at 70fps, yet the CPU load in dom0 is only 0%, as most operations are offloaded to the graphics card.