Thanks for pointing that out. I got fed up with repeating it every time someone came along with requests to support yet another file format.
As to OneNote, in the past Microsoft has produced viewers for popular formats, I don't think even Microsoft has come out with a view for .one files.
If we are asking for support for things like OneNote, I prefer Evernote.
But both of these hold messages in databases rather than as separate files. Surely that must complicate the issue. X1 does do databases, but it must be even more dependent on third party support.