Lotus Worksheet (.wk1)
The WK1 file extension, short for Lotus Worksheet, was used by the Lotus 1-2-3 spreadsheet software developed by Lotus Development Corporation and later acquired by IBM. These files stored data in a tabular format with cells organized by rows and columns, enabling users to perform data analysis and compute formulas efficiently. Although Lotus 1-2-3 has been discontinued, WK1 files can still be opened by some versions of Microsoft Excel and other compatible software like OpenOffice Calc. However, support for WK1 files was dropped in Excel 2007 and later versions.