What are some alternatives?
When comparing Gnumeric and SpreadsheetConverter.com, you can also consider the following products
LibreOffice - Calc - LibreOffice Calc is the spreadsheet program you've always needed. A fork of OpenOffice.
SpreadsheetWEB - SpreadsheetWEB is a no-code platform that helps businesses translate their collective Microsoft Excel expertise into robust web applications with limited or no reliance on IT resources.
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.
Google Sheets - Synchronizing, online-based word processor, part of Google Drive.
Appizy - Convert spreadsheet to web application