.XLS File Extension Description:

A user without Excel can still open excel files by downloading Microsoft’s free excel viewer. File extension XLS is applied in Microsoft Excel spreadsheet applications. Microsoft Excel is very similar to many other spreadsheet applications that store information to be viewed and edited on several platforms.

The programs that open Microsoft Excel and XLS files on the Mac and windows OSs installed with MSOffice application. Microsoft Excel files contain information similar to that provided by databases as well as formulas, graphs, charts and images that are necessary in presentation of reports.

Learn more about .XLS Files here: http://xls.file-extension-library.com/