Microsoft Office Version and Windows Version Compatibility Chart

LibreOffice and OpenOffice are free (these are different versions of the same suite of programs) and can read and write MS Office files.

I've used Open Office, more recently LibreOffice for years. It's fine for word processing, presentations, and uncomplicated spreadshhets. A 'power' user of office - e.g. a macro user - will find it inadequate.

I suspect that a user of, say Office 2000, who doesn't want any changes to the 16 year old interface will be unhappy with any alternative. But running XP, connected to the internet, is just asking to join a botnet, as my link (20 Jun 16 - 02:08 AM) explained:

Machines can be recruited into botnets against their users' will through security vulnerabilities in the software they are running. Windows XP's popularity and lengthening list of known vulnerabilities might make it an excellent source of recruits.