KS is the file extension associated with the older Microsoft Works office suite. KS files were used by the spreadsheet management application that was part of the package. This application saved spreadsheets in KS files. The structure of these documents was characteristic of this type of files. The KS file consisted of columns and rows that made up the cells of the worksheet. These files were replaced with WKS files in later versions of Microsoft Works.

Works is the smaller office suite from Microsoft. It is no longer developed and KS files are considered obsolete.