Google "Spreadsheet"

Starting this morning (June 6) you can sign up for an invitation to join "Google Spreadsheets", an on-line servbice that will allow you to:

Create basic spreadsheets from scratch.
You can start from scratch and do all the basics, including changing the number format, sorting by columns, and adding formulas.

Upload your spreadsheet files.
Upload spreadsheets or worksheets from CSV or XLS format – all your formulas and formatting will come across intact.

Familiar desktop feel makes editing a breeze.
Just click the toolbar buttons to bold, underline, change the font, change the cell background color and more. (...)

Choose who can access your spreadsheets.
Just enter the email addresses of the people you want to share a given document, and then send them a message.

Share documents instantly.
People with whom you share a given spreadsheet can access it as soon as they sign in.

Edit with others in real time.
Multiple people can edit or view your spreadsheet at the same time as you – their names will appear in an on-screen chat window.