How to collaborate on/share a document with someone on Windows?

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http://askubuntu.com – I want to edit a document in online collaboration with other person. I'm using Ubuntu, the other is on Windows. Do I understand it right that the only way is that the Windows user would need to go through the web always? (Because "Share" service is only users with Nautilus and Ubuntu). Is it so? I got (I think) the part where I right-click on "share" and provide his email and so on. I would like to know how would the usage experience be for Win user - would it sync his folder comfortably or would he always need to go to web account and download newest version? (HowTos)