Sheetster is described as 'web-based spreadsheet (i.e. Excel) editing, viewing and sharing tool. Upload your spreadsheets (or create new ones), edit spreadsheets in Excel-like interface, and securely share them with others (friends, coworkers, family, etc)' and is a Spreadsheet app in the office & productivity category. There are more than 25 alternatives to Sheetster, not only websites but also apps for a variety of platforms, including Windows, Mac, Linux and iPad. The best alternative is LibreOffice - Calc, which is both free and Open Source. Other great sites and apps similar to Sheetster are Microsoft Office Excel, Google Drive - Sheets, Gnumeric and EtherCalc.
LibreOffice Calc is the spreadsheet program you've always needed. A fork of OpenOffice.org Calc, professional data miners and number crunchers will appreciate its comprehensive range of advanced functions.
EtherCalc is a web spreadsheet. Your data is saved on the web, and people can edit the same document at the same time. Everybody's changes are instantly reflected on all screens. Work together on inventories, survey forms, list management, brainstorming sessions and more!
Create gorgeous spreadsheets with Numbers for Mac. Get started with one of many Apple-designed templates for your home budget, checklist, invoice, mortgage calculator, and more. Add tables, charts, text, and images anywhere on the free-form canvas.
Spread32 is a mini-Excel with all of the basic features that you would expect in a competent spreadsheet program. Run macros, draw objects, generate charts, calculate functions and formulas, its all here. And it reads and writes xls, csv, text, and pxl formats.