Lotus 1-2-3 is a spreadsheet program from Lotus Software (now part of IBM). It was IBM PC's first killer application; its huge popularity in mid-1980s contributed significantly to the success of IBM PC in the corporate environment.
1-2-3 was originally written by a graduate student at Harvard Business School, who reportedly sold it to Lotus for less than $200,000.
1-2-3 was released on January 26, 1983, started outselling then most popular VisiCalc the very same year, and for a number of years it was the leading spreadsheet for the DOS operating system.
Lotus 1-2-3 came with a separate program to print graphs and charts, but this could not then be run at the same time as the spreadsheet. It had keyboard-driven pop-up menus as well as one-key commands, making it fast to operate. It was also user-friendly, introducing what might have been the first ever context-sensitive help.
Macros and add-ins (introduced in version 2.0) attributed much to 1-2-3's popularity, allowing dozens of outside vendors to sell macro packages and add-ins ranging from dedicated financial worksheets to full-fledged word processors. (In the single-tasking MS-DOS 1-2-3 was sometimes used as a complete environment.) Lotus 1-2-3 supported EGA and later VGA graphics. Early versions used the filename extension "WKS", which was changed for version 2.0 to "WK1".
Lotus 1-2-3 has been the subject of several user interface copyright court cases in the US. Most notably the program Quattro Pro from Borland used the same keyboard commands, prompting Lotus to claim infringement of its copyright on the "look and feel" of its interface.
The rise of Microsoft Windows in the personal computer market was accompanied by the rise in Microsoft's competing spreadsheet, Excel, and it gradually usurped the position of 1-2-3. Being loyal to OS/2, Lotus was slow to embrace Windows. Additionally, several versions of 1-2-3 were available concurrently, each with different set of functionality and slightly different interface.
1-2-3's intended successor, Lotus Symphony, had simultaneous update of spreadsheet, graph and word processor windows, but was short-lived. 1-2-3 migrated to the Windows platform, where it remains available as part of Lotus SmartSuite.