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There are apps for all platforms except Linux, but you could use the web interface there.

I'm using it on Windows (desktop version, not the app) and Android and it works pretty well.

Yep. The Metro app on Win8 has a very poor UX, but the desktop version (also available on WinRT) is fantastic.

The OSX native app seems to have parity more or less with the Windows one. I use it at work and haven't had any issues.