CubeWeaver - CubeWeaver is a collaborative multidimensional spreadsheet software especially useful for financial planning, financial modelling, budgeting, reporting and what-if simulations.
EtherCalc - EtherCalc is a web spreadsheet.
FlexiSheet - FlexiSheet is a multi-dimensional spreadsheet in the spirit of Lotus Improv.
XCubes - Multidimensional spreadsheet for financial simulation, planning, reporting, marketing analysis etc.
LibreOffice - Calc - LibreOffice Calc is the spreadsheet program you've always needed. A fork of OpenOffice.
Pyspread - pyspread is a non-traditional spreadsheet application that is based on and written in the programming language Python.