Definition(en): Lotus 1-2-3 Workbook is a spreadsheet program produced by the Lotus Software Group (later acquired by IBM). The original release was in 1983 and it has been discontinued since 2013. The original 1-2-3 files have .wks extensions. Version 2.0 originally used a .wk1 extension but this was changed quickly to .wk2 and after this the number in the extension corrolates with the version number. Some later versions have the extension .123