Desktop application allowing backup (syncing) of local folders onto (multiple) Cloud Storage ?

Question

I find it odd that this question hasn't been asked already... I thought there were more people paranoid that I am...

Anyway, is there any desktop application, that allows me to backup a given folder to a (Cloud) storage service (Amazon / Rackspace / ...) ?

Note: I am not looking for companies providing backup solutions, there are plenty.

I am looking for this combination instead:

1. Free application (open source)
2. Ability to chose storage providers (preferrably multiple)
3. Bi-directional sync.

Any pointers would be really helpful !

Answer 1

rsync.

Answer 2

there is this tool called duplicity which use librsync and syncronize to amazon s3