What are some alternatives?
When comparing Keikai and SpreadsheetWEB, you can also consider the following products
EtherCalc - EtherCalc is a web spreadsheet.
SpreadsheetConverter.com - Use online spreadsheets, smart forms and beautiful charts in your blog or website. Put your booking and order forms online. Show live charts. Change any cell and the online spreadsheet or live chart immediately updates itself.
Microsoft Office Excel - Microsoft Office Excel is a commercial spreadsheet application.
Publisheet - Publish your Excel sheets to the web as dynamic web applications with formula support.
LibreOffice - Calc - LibreOffice Calc is the spreadsheet program you've always needed. A fork of OpenOffice.
Excel Online - Excel Online, part of Office Online, is the online version of Microsoft Excel.