From Gamasutra: A very interesting read compiled by Peter Rakos, in which he explains how to begin experimenting with Microsoft Excel for game development purposes. As previously mentioned by the2bears, there is also a vertical shooter project released by Shadow Slash which runs entirely from an Excel spreadsheet macro. Security settings may have to be set to medium in order to get this application working. (under Tools, Macro, Security)

Controls for DEX-EV are: Z for shoot, hold X to move your ship at a slower pace or to activate the special attack, and press C for bombs. The game also sports three different power-ups for the purposes of upgrading your weapons or to generate a protective shield around your ship. (direct download link)

Gamasutra - Feature: Microsoft Excel As A 'Revolutionary Game Engine' DEX-EV