VisiCalc is the first ever computer spreadsheet. Dan Bricklin, inventor of the spreadsheet, received permission from Lotus who now owns the copyright for VisiCalc to allow him to offer it for free on his website. The actual executable weighs in at a paltry 27 kilobytes, and would run on a PC from 1981 - in fact it is virtually identical to the one that shipped for DOS 1.0. The only difference is that the copy protection has been removed.