There are certainly alternatives. Here are the ones I have tested quite thoroughly:
- LibreOffice
- WPS Office
- FreeOffice/Softmaker Office
- OnlyOffice Desktop
None are fully compatible from a formatting or functionality perspective. None is a clear winner as to the most compatible. They all have different strengths and weaknesses. They all struggle with the advanced functionality in Excel and Powerpoint.
If you are talking about Microsoft Word documents most of them will be fine with one caveat. You need to have the Microsoft fonts. If you don't, formatting will be off.
There are other alternatives.
- Office 365 Online which is a free cloud version of Office. Compatibility is good but the feature set is a bit cut down.
- If you have at least 8GB of total RAM, you could run a Windows VM.