LibreOffice is/was a "fork" of OpenOffice (which started off as Sun's StarOffice).
OpenOffice is moribund/no longer being developed. Forget it.
LibreOffice is free (please donate a few bucks when you download it), cross-platform, excellent, and there are now very few incompatibilities with MSOffice.
You can save your docs in MSOffice format if you like, though the OpenDocument Format (ODF), is an ISO/IEC standard that is overtaking the MSOffice formats worldwide.
Use it and love it.
Mac