I’ve just released a Microsoft Excel Viewer that runs in IntelliJ IDEA and other JetBrains IDE’s such as Android Studio or PyCharm.
It can open xlsx, xls and csv files, copy text from the spreadsheet or open the spreadsheet in an office suite.
To run it, download the free Applet Runner plugin from JetBrains marketplace and execute the free Excel Viewer applet located at https://www.japplis.com/applet-runner/office/excel-viewer.html.