Microsoft Office used to create the spreadsheet files in the XLS format. These files were created by the Microsoft Excel component of the Office suite. Later the new versions of Microsoft Excel started a new format that uses XML based XLSX file format. Then there are some other file formats that can also carry data in tabular format such as the CSV and ODS files.
In order to create these files, we need either Microsoft Excel (which is part of Microsoft Office suite), OpenOffice or Libre Office. The latter two of these are both open-source and freely available for multiple platforms. However, if you do not install these on your system just to view the XLS, XLSX, CSV and ODS files, then you can try another freeware called Bytescout XLS Viewer.
Bytescout XLS Viewer is a free software for Windows and macOS. It is free for personal use only. If you use it for commercial locations then you have to purchase a license. During the installation it offers to associate itself with all the supported files, namely XLS, XLSX, CSV and ODS. It is recommended that you associate these files with XLS Viewer. Without association opening these files will be a little difficult.
Once you have installed Bytescout XLS Viewer on your PC (and associated it with all the supported files), you can simply double-click on any XLSX or XLS file to open it in Bytescout XLS Viewer and view it. There are no options in the Bytescout XLS Viewer and the menubar simple contains an “Open” command and an “Exit” command.
If you do not want to install full Office suite on your PC then you can use the small free Bytescout XLS Viewer. It can display all sorts of XLS and XLSX files but does not allow any changes to be made.
You can download Free Bytescout XLS Viewer from https://bytescout.com/products/enduser/misc/xlsviewer.html.