The Excel product team is offering the new Excel Web App as part of the browser-based Microsoft Office Web Apps. The Excel Web App is a companion to the Excel client, and it provides users with the ability to create, view, edit, and collaborate on Excel workbooks in several supported browsers.
The following excellent posts (written by the Excel Services product group PMs) talk about what the Excel Web App is, how it works in your browser, and provide step-by-step instructions about editing in the Excel Web App:
· Excel Web App 2010 Overview
· Editing in Excel Web App – Part 1
· Collaborative Editing Using Excel Web App
· More about collaborative editing in Excel Web App