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Had a look on their website and they say it doesn’t just work with Dropbox. From their FAQ page:

‘… you can use SecretSync with any synchronization product that uses a local folder on your computer. We have users who use SugarSync rather than Dropbox. Since both tools behave in basically the same way, i.e. picking up changes in a regular folder on your computer, SecretSync is compatible with either’.

That’s an interesting encryption alternative. I’m currently using Cloudfogger for this.