Has a colleague sent you an email with an XLSX file attached? It’s not a strange new type of file for some new piece of software: it’s just a newer Excel file type. But if you have an older version of Excel, earlier than 2007, then you might not be able to open it. Here is an update from Microsoft that will allow you to open XLSK files in older versions of Excel. Additionally, here are several other free and easy ways to open XLSK files.