What are some alternatives?
When comparing Sheetgo and Excel Online, you can also consider the following products
Google Sheets - Synchronizing, online-based word processor, part of Google Drive.
EtherCalc - EtherCalc is a web spreadsheet.
TableEdit - free mac app to view and edit spreadsheets
Microsoft Office Excel - Microsoft Office Excel is a commercial spreadsheet application.
LibreOffice - Calc - LibreOffice Calc is the spreadsheet program you've always needed. A fork of OpenOffice.
Apache OpenOffice Calc - Calc, part of the https://alternativeto.