Numbler is a web-based spreadsheet app that enables collaboration with others in real time. It works like most any spreadsheet but is has far fewer features, so it's probably best suited for keeping simple data that many people need to access and change at the same time. Numbler spreadsheets are identified by URL alone, so you don't have to register an account and it's easy to invite others to use your spreadsheet. It also has import and export features, including XML and CSV files such as Excel exports. Numbler is of course in beta.