I don't even have a copy of MarinerWrite on my two computers. My wife
does still use it occasionally, but you know how difficult it can be to ever change a woman's mind...
She actually uses Word and I shudder any time she asks me how to do some thing or even explain where a menu item might be! Heaven help the noobie trying to decipher the hundreds of tiny icons!
I very rarely write on any word processor now. I do use TextEdit almost every day. If I need to create/send (even snail mail!) something, I'll use Pages (the original version, of course). The fact is, the world standard text document file format is .doc/.docx, so it's probably wise to always save at least one copy of anything important in that format. Personally, I find .rtf to be just as useful and universal.
Proprietary formats (although .doc/x is one) are always dangerous. Who would have thought the Encyclopedia Britannica would ever become obsolete?! OK, bad example, most folks younger than 30 have never even heard of that publication. I doubt they have any idea where the "pedia" part of Wikipedia comes from.