Windows 7
A demo of the next generation Windows kernel, strip naked, codenamed "Windows 7" (Microsoft really needs to put more work in these names. Just a random thought, something along the line of "iWin" might work...).
The OS ran under Virtual PC, and this allowed Traut to show the audience exactly how many resources it was consuming: about 25MB on disk (compare with 14GB for a full Vista install) and 40MB of RAM. The OS booted up in about 20 seconds inside Virtual PC.