Sounds like you're looking for ownCloud. It's still under heavy development but the file storage functions work very well and it's accessible on Mac, Windows & Linux via webdav and from everywhere else via a web interface. There are also a couple of mobile apps in the works and it runs on a standard LAMP stack. http://owncloud.org/index.php/Main_Page And a blog post about the current status: http://owncloudtest.blogspot.com/2011/06/owncloud-20-just-merged-with.html
It's really great to see this. One of linux's greatest weaknesses is the amount of duplication that happens. Sometimes it's necessary but a lot of the time the community would be better served by everybody working together instead of against each other. This is one of those times and I applaud the beryl and compiz devs for realizing that and having the good sense to swallow a little bit of their pride on both sides. I'm looking forward to the great things that will come out of this.