What are some alternatives?
When comparing dhtmlxSpreadsheet and LibreOffice - Calc, you can also consider the following products
ag-Grid - The best HTML5 datagrid in the world
Google Sheets - Synchronizing, online-based word processor, part of Google Drive.
EtherCalc - EtherCalc is a web spreadsheet.
Microsoft Office Excel - Microsoft Office Excel is a commercial spreadsheet application.
TableEdit - free mac app to view and edit spreadsheets