> 1. For a Linux user, you can already build such a system yourself quite trivially by getting an FTP account, mounting it locally with curlftpfs, and then using SVN or CVS on the mounted filesystem. From Windows or Mac, this FTP account could be accessed through built-in software.
Trivially use three different systems to simulate some type of not quite automatic syncing.
Why do Linux users often claim something is "trivial" and then go on to list obscure commands and software packages that have to be tied together in just the right way? To me that's "possible to do", not "trivial to do".