Dropbox - Secure backup, sync and sharing made easy. - interesting file sync service - the client is written in Python (though closed source in the delivery). Initially, I was a bit annoyed because it doesn't say which systems it works on - and my work Mac on which I'm currently testing it is still on 10.3.9. And yes, it actually works. Ok, if it even supports 10.3.9, you can ignore system version specifications ... (although, I've heard there are still 10.2 users)