Microsoft office

I'm rather impressed with the MS Office compatibility and comparability of FreeOffice - https://www.freeoffice.com/ The free version trails the paid by one release... seems like a fair compromise. It's not pure FOSS, so purists might not like it, but it really gets the job done, especially with rountripping documents. There are always corner cases where things go boink, but hell... things even go off the deep end between versions of MSO.