LibreOffice - Calc - LibreOffice Calc is the spreadsheet program you've always needed. A fork of OpenOffice.
EtherCalc - EtherCalc is a web spreadsheet.
Excel Formula Beautifier - Beautifies Excel to JavaScript/JSON format.
XCubes - Multidimensional spreadsheet for financial simulation, planning, reporting, marketing analysis etc.
Pyspread - pyspread is a non-traditional spreadsheet application that is based on and written in the programming language Python.
Vole Office - A light Microsoft Word and Excel editor.