After my previous post on three web-based word processor software, here are three web-based spreadsheet software: Num Sum, iRows, and Number. My first impression give iRows a vote!
Num Sum is advertised as easy, sharable web spreadsheets. With it you can (1) track your records, lists and data online, (2) share with other users you decided, (3) connect with other users who have similar interests. Example uses of Num Sum are: team schedules, home budgeting, online stock portfolio, and recording project progress.
iRows is the Web based online spreadsheets. With it you can (1) manage your data online, access it anywhere, anytime, (2) share your data others, (3) display your data on any web site, change it here, and all sites change automatically, (4) compute, chart, and analyze your data online.
Number (Beta) is the web based spreadsheet that enables instantaneous collaboration with anyone on your project team. With it you and your-invited users can work with a spreadsheet, view changes in real time, and discuss changes.