StarOffice was the original "knock off" in about 1985 for CP/M and MS-DOS.
Then there was SunOffice
OpenOffice
LibreOffice
It can read & write many MS Office Format and has "native formats". IMO "Writer" manages paragraph, character, table, list, graphic and page styles better than MS Word. Sometimes imports / exports are bit strange and it may be good to edit formats/styles on imports.
It's best to use ODT to edit and only Save AS to export to people /apps needing DOC or DOCX.
You might do some less common things differently in Writer than Word.
The Graphs are easier to manage in the Spreadsheet than in Excel. Though I use Gnumeric for simple spreadsheets.
MS never did much with Powerpoint after they bought it. Impress is less annoying.
So anyway while LibreOffice can be used to import and edit existing work, and can Save As for Word and apps wanting Word format, and Export (decent HTML and PDF export), it's not a knock off or clone.
You can use traditional menus, docked or floating, or Ribbon like interface.
I'd not go back to MS Office. Esp the versions with Ribbon or MS's clone of Google Docs, the Office 365.
The last decent MS Office was 2003 and all future emphasis is on the Cloud and Office 365/Subscription.
I used LibreOffice for about a year on windows instead of MS Word & Excel before Linux only. I used to teach MS Office.
I've used Word for Windows since Ver 2.0a in the 1990s.
I'd used Wordstar, Word Prefect and MS Word on CP/M and MS-DOS (1981 - 1992)
I found Word 2002 / XP better than OpenOffice in the years before LibreOffice became the replacement.
OpenOffice as such is gone
https://en.wikipedia.org/wiki/OpenOffice.org
Some parts of the original OpenOffice make no sense now:
Vector: Inkscape better
Images: Gimp better
Database: MySql, MariaDB or SqlLite
Image conversion / processing / display: ImageMagick (servers or workstations)
I've now written nearly 30 books and other docs and over 2 million words in LibreOffice Writer.