Google Sheets - Synchronizing, online-based word processor, part of Google Drive.
SSuite Axcel Professional Spreadsheet - This powerful and professional spreadsheet has all the tools you need to calculate, analyse, summarize, and present your data in numerical reports or colourful graphics.
Sheetgo - Connect spreadsheets. Automate your work.
EtherCalc - EtherCalc is a web spreadsheet.
Excel Online - Excel Online, part of Office Online, is the online version of Microsoft Excel.
Keikai - Effortlessly Build Spreadsheet-driven Web Apps