Google Sheets - Synchronizing, online-based word processor, part of Google Drive.
EtherCalc - EtherCalc is a web spreadsheet.
Aspose.Cells for Cloud - Aspose.Cells for Cloud is a REST based API for processing spreadsheets in the cloud.
Gnumeric - Gnumeric
Simple Spreadsheet - Simple Spreadsheet
LibreOffice - Calc - LibreOffice Calc is the spreadsheet program you've always needed. A fork of OpenOffice.