SoftMaker FreeOffice is a free Microsoft Office-compatible productivity suite.
The package includes a word processor (TextMaker), spreadsheet (PlanMaker) and presentation tool (SoftMaker), and each of these can open both the old-style and Office 365/2010 files for their equivalent Microsoft application (DOC and DOCX/ DOCM/ DOTX/ DOTM, XLS and XLSX, PPT and PPTX, and so on). And reasonably accurately, too, although there are occasional problems with more complex documents.
If you're not a fan of the Microsoft Office ribbon then the SoftMaker FreeOffice interface may appeal, as it offers a classic style (a ribbon is available an option) to the more conventional menus and toolbars.
And the suite has plenty of useful extra features, including a handy "Export to PDF" option on every File menu, and the ability to be installed on a USB flash drive.
If you need more, though, SoftMaker is hoping you'll upgrade to the commercial version, SoftMaker Office 2018, which can be yours from $99.95. The commercial version has a more flexible user-interface, including a dark mode, includes a 64-bit version, advanced document creation, advanced presentations and much more.
Note that you need a personal serial code to use FreeOffice, which you can obtain here.
SoftMaker FreeOffice is a capable free Office-compatible productivity suite.