Spreadsheet (Lotus 1-2-3 v. 4)
The WK4 file extension is primarily associated with a spreadsheet file for Lotus 1-2-3 v. 4. Lotus 1-2-3 was the second spreadsheet application, developed after VisiCalc and before Microsoft Excel. It was the first to introduce cell names and macros. IBM bought Lotus in 1995.
See questions and answers about working with spreadsheets.