You could use Libre Office Calc and save the tables in csv-format (Comma Separated Values). That's enough for basic tables if you don't need to save, for example, the size of rows/columns, formatted text (bold, italics), etc. Those files are supported by both Libre Office and MS Office.
Libre Office can save in Microsoft's proprietary file formats as well (Calc/Excel => xlsx, Write/Word => docx) , but since the formats have been reverse engineered without support from Microsoft, the saved files might look a bit different on Libre Office than on MS Office.
I'm not sure if MS Office supports the Libre Office file formats. Since those are open source, I'd think MS has added them in their office suite. So, if you...