TouchWall is a touch screen hardware setup created by Microsoft; the corresponding software to run TouchWall, which is built on a standard version of Vista, is called Plex.
TouchWall consists of three infrared lasers that scan a surface. A camera notes when something breaks through the laser line and feeds that information back to the Plex software. Early prototypes were made, simply, on a cardboard screen.
TouchWall and Plex are superficially similar to Microsoft Surface, a multi-touch table computer that was introduced in 2007. However, TouchWall is a fundamentally simpler mechanical system, and is also significantly cheaper to produce (hundreds of dollars vs the $10,000 cost of Surface).
A demonstration of Microsoft Touchwall.Added: 5/15/08
Michael Arrington using Microsoft Touchwall.Added: 5/15/08