A spreadsheet program is used to facilitate the presentation and computation of data that contains numbers. Normally, spreadsheets are created for financial statements, budgets, report cards, etc. where the numbers can be edited with the formulae (such as averages and totals) in the spreadsheet recomputing automatically each time changes are made.
The earliest successfull spreadsheet software was Visicalc, followed by the venerable Lotus 123. Borland also joined the fray with its Quattro Pro. Microsoft Excel is now by far the most featureful and widely used spreadsheet program (but available mainly on Windows) but open source efforts such as OpenOffice.org and KOffice and Gnumeric are catching up and at least one study suggests Gnumeric has better mathematical algorithms. OpenOffice's spreadsheet program, OpenOffice Calc, is one of the most popular spreadsheet programs on Linux distributions.
Nowadays, spreadsheet programs are usually bundled into Office Suites.