OFFICE

LIBRE OFFICE SUITE (Windows, Mac, Linux)
As good as  MS Office in my experience. Very good converter for different formats (it can be used to easily convert between different MS Office editions). It does not
have some of the bells and whistles of MS Office, but I for one rarely use these. And it does not have the irritatingly default  tab stops of MS Word (albeit defeatable
with difficulty). Its equation editor is not as good as Mathtype BUT as good (perhaps better) than that in  MS Office 365.
NOTE (1/7/22): It appears that Microsoft defaults to its Edge app if you use Firefox. I have had success using Google Chrome.

 FREE-OCR
 Does not do well for tables and math but neither do any other OCR free versions I have tried.  Allows figures to be copied and pasted into Word.

JABREF (Windows)
Bibliography software for Windows (web reader reviews say EndNotes freeware is terrible compared with this, but these reviews may of course come from competitors...)

JABREF (Mac OS-X)

BIBDESK (Mac OS-X)
Bibliography software

ZOTERO
Bibliography Organizer

LYX WORD PROCESSOR
This requires two downloads:
(1) LaTeX application HERE
(2) Lyx application HERE.
Installation of Lyx will take some time (lot's of checking that is reassuring)

SciDAVis  (Excellent plotting from tabulated data  (rows can be added to the default 30 one at a time) HERE.