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