Ubuntu officially released their Mac client for the Ubuntu One service, here is a summary of what you get:
- 5GB Free and other plans are available
- Works on Mac, PC, iOS, Android, and of course Linux
- Share files via email, Facebook, Twitter
- Buy music and get 20GB and 6 months of streaming (that part is weak)
Follow the link and try it out. Works with OS X 10.6 or later.